Merge rust-bitcoin/rust-bitcoin#1018: Add more documentation to some core types

1875c91 Extend docstring for more types (Dawid Ciężarkiewicz)
325ea8f Add "Relevant BIPs` to `Address` (Dawid Ciężarkiewicz)
7c2ca3d Add `BlockHeader` Bitcoin Core reference link (Dawid Ciężarkiewicz)
f4922f6 Update `BlockHeader::version` documentation (Dawid Ciężarkiewicz)

Pull request description:

  This is meant to make it more educational, and handy even for experienced developers.

  A first step to make https://docs.rs/bitcoin (or `cargo doc --open`) a go-to place for
  convenient Bitcoin documentation.

ACKs for top commit:
  tcharding:
    tACK 1875c91
  apoelstra:
    ACK 1875c91
  sanket1729:
    utACK 1875c91. Thanks for doing this.

Tree-SHA512: 8457e120f9979bfd95e55e8b18faf6131610aa2241f8e5fc4630fe61dc7e16ddfc35fb6eff46339804016db7b176465943cc0c02d84dcf478ed55da9f5e06fc5

Author: ChallengeDev210

src/blockdata/block.rs

@@ -37,13 +37,26 @@ use crate::blockdata::constants::{max_target, WITNESS_SCALE_FACTOR};
 use crate::blockdata::script;
 use crate::VarInt;
 
-/// A block header, which contains all the block's information except
-/// the actual transactions
+/// Bitcoin block header.
+///
+/// Contains all the block's information except the actual transactions, but
+/// including a root of a [merkle tree] commiting to all transactions in the block.
+///
+/// [merkle tree]: https://en.wikipedia.org/wiki/Merkle_tree
+///
+/// ### Bitcoin Core References
+///
+/// * [CBlockHeader definition](https://github.com/bitcoin/bitcoin/blob/345457b542b6a980ccfbc868af0970a6f91d1b82/src/primitives/block.h#L20)
 #[derive(Copy, PartialEq, Eq, Clone, Debug)]
 #[cfg_attr(feature = "serde", derive(Serialize, Deserialize))]
 #[cfg_attr(feature = "serde", serde(crate = "actual_serde"))]
 pub struct BlockHeader {
-    /// The protocol version. Should always be 1.
+    /// Originally protocol version, but repurposed for soft-fork signaling.
+    ///
+    /// ### Relevant BIPs
+    ///
+    /// * [BIP9 - Version bits with timeout and delay](https://github.com/bitcoin/bips/blob/master/bip-0009.mediawiki) (current usage)
+    /// * [BIP34 - Block v2, Height in Coinbase](https://github.com/bitcoin/bips/blob/master/bip-0034.mediawiki)
     pub version: i32,
     /// Reference to the previous block in the chain.
     pub prev_blockhash: BlockHash,
@@ -156,8 +169,17 @@ impl BlockHeader {
     }
 }
 
-/// A Bitcoin block, which is a collection of transactions with an attached
-/// proof of work.
+/// Bitcoin block.
+///
+/// A collection of transactions with an attached proof of work.
+///
+/// See [Bitcoin Wiki: Block][wiki-block] for more information.
+///
+/// [wiki-block]: https://en.bitcoin.it/wiki/Block
+///
+/// ### Bitcoin Core References
+///
+/// * [CBlock definition](https://github.com/bitcoin/bitcoin/blob/345457b542b6a980ccfbc868af0970a6f91d1b82/src/primitives/block.h#L62)
 #[derive(PartialEq, Eq, Clone, Debug)]
 #[cfg_attr(feature = "serde", derive(Serialize, Deserialize))]
 #[cfg_attr(feature = "serde", serde(crate = "actual_serde"))]

src/blockdata/script.rs

@@ -47,7 +47,20 @@ use crate::util::taproot::{LeafVersion, TapBranchHash, TapLeafHash};
 use secp256k1::{Secp256k1, Verification, XOnlyPublicKey};
 use crate::schnorr::{TapTweak, TweakedPublicKey, UntweakedPublicKey};
 
-/// A Bitcoin script.
+/// Bitcoin script.
+///
+/// A list of instructions in a simple, [Forth]-like, stack-based programming language
+/// that Bitcoin uses.
+///
+/// [Forth]: https://en.wikipedia.org/wiki/Forth_(programming_language)
+///
+/// See [Bitcoin Wiki: Script][wiki-script] for more information.
+///
+/// [wiki-script]: https://en.bitcoin.it/wiki/Script
+///
+/// ### Bitcoin Core References
+///
+/// * [CScript definition](https://github.com/bitcoin/bitcoin/blob/d492dc1cdaabdc52b0766bf4cba4bd73178325d0/src/script/script.h#L410)
 #[derive(Clone, Default, PartialOrd, Ord, PartialEq, Eq, Hash)]
 pub struct Script(Box<[u8]>);
 

src/blockdata/transaction.rs

@@ -53,6 +53,10 @@ const UINT256_ONE: [u8; 32] = [
 ];
 
 /// A reference to a transaction output.
+///
+/// ### Bitcoin Core References
+///
+/// * [COutPoint definition](https://github.com/bitcoin/bitcoin/blob/345457b542b6a980ccfbc868af0970a6f91d1b82/src/primitives/transaction.h#L26)
 #[derive(Copy, Clone, Debug, Eq, Hash, PartialEq, PartialOrd, Ord)]
 pub struct OutPoint {
     /// The referenced transaction's txid.
@@ -188,7 +192,15 @@ impl ::core::str::FromStr for OutPoint {
     }
 }
 
-/// A transaction input, which defines old coins to be consumed
+/// Bitcoin transaction input.
+///
+/// It contains the location of the previous transaction's output,
+/// that it spends and set of scripts that satisfy its spending
+/// conditions.
+///
+/// ### Bitcoin Core References
+///
+/// * [CTxIn definition](https://github.com/bitcoin/bitcoin/blob/345457b542b6a980ccfbc868af0970a6f91d1b82/src/primitives/transaction.h#L65)
 #[derive(Clone, PartialEq, Eq, PartialOrd, Ord, Debug, Hash)]
 #[cfg_attr(feature = "serde", derive(Serialize, Deserialize))]
 #[cfg_attr(feature = "serde", serde(crate = "actual_serde"))]
@@ -222,7 +234,17 @@ impl Default for TxIn {
     }
 }
 
-/// A transaction output, which defines new coins to be created from old ones.
+/// Bitcoin transaction output.
+///
+/// Defines new coins to be created as a result of the transaction,
+/// along with spending conditions ("script", aka "output script"),
+/// which an input spending it must satisfy.
+///
+/// An output that is not yet spent by an input is called Unspent Transaction Output ("UTXO").
+///
+/// ### Bitcoin Core References
+///
+/// * [CTxOut definition](https://github.com/bitcoin/bitcoin/blob/345457b542b6a980ccfbc868af0970a6f91d1b82/src/primitives/transaction.h#L148)
 #[derive(Clone, PartialEq, Eq, PartialOrd, Ord, Debug, Hash)]
 #[cfg_attr(feature = "serde", derive(Serialize, Deserialize))]
 #[cfg_attr(feature = "serde", serde(crate = "actual_serde"))]
@@ -240,7 +262,19 @@ impl Default for TxOut {
     }
 }
 
-/// A Bitcoin transaction, which describes an authenticated movement of coins.
+/// Bitcoin transaction.
+///
+/// An authenticated movement of coins.
+///
+/// See [Bitcoin Wiki: Transaction][wiki-transaction] for more information.
+///
+/// [wiki-transaction]: https://en.bitcoin.it/wiki/Transaction
+///
+/// ### Bitcoin Core References
+///
+/// * [CTtransaction definition](https://github.com/bitcoin/bitcoin/blob/345457b542b6a980ccfbc868af0970a6f91d1b82/src/primitives/transaction.h#L279)
+///
+/// ### Serialization notes
 ///
 /// If any inputs have nonempty witnesses, the entire transaction is serialized
 /// in the post-BIP141 Segwit format which includes a list of witnesses. If all

src/util/address.rs

@@ -547,6 +547,15 @@ impl<'a> fmt::Display for AddressEncoding<'a> {
 }
 
 /// A Bitcoin address.
+///
+/// ### Relevant BIPs
+///
+/// * [BIP13 - Address Format for pay-to-script-hash](https://github.com/bitcoin/bips/blob/master/bip-0013.mediawiki)
+/// * [BIP16 - Pay to Script Hash](https://github.com/bitcoin/bips/blob/master/bip-0016.mediawiki)
+/// * [BIP141 - Segregated Witness (Consensus layer)](https://github.com/bitcoin/bips/blob/master/bip-0141.mediawiki)
+/// * [BIP142 - Address Format for Segregated Witness](https://github.com/bitcoin/bips/blob/master/bip-0142.mediawiki)
+/// * [BIP341 - Taproot: SegWit version 1 spending rules](https://github.com/bitcoin/bips/blob/master/bip-0341.mediawiki)
+/// * [BIP350 - Bech32m format for v1+ witness addresses](https://github.com/bitcoin/bips/blob/master/bip-0350.mediawiki)
 #[derive(Clone, PartialEq, Eq, PartialOrd, Ord, Hash)]
 pub struct Address {
     /// The type of the address.