docs: create documentation for all features

Enable the `--all-features` flag for docs.rs for the crates that contain
non-default features.

Closes #197.

Author: vmx

Cargo.toml

@@ -15,6 +15,9 @@ documentation = "https://docs.rs/multihash/"
 edition = "2021"
 rust-version = "1.64"
 
+[package.metadata.docs.rs]
+all-features = true
+
 [features]
 default = ["std"]
 std = ["unsigned-varint/std", "alloc"]

codetable/Cargo.toml

@@ -8,6 +8,9 @@ edition = "2021"
 
 # See more keys and their definitions at https://doc.rust-lang.org/cargo/reference/manifest.html
 
+[package.metadata.docs.rs]
+all-features = true
+
 [features]
 default = ["std"]
 std = ["blake2b_simd?/std", "blake2s_simd?/std", "blake3?/std", "digest?/std", "sha1?/std", "sha2?/std", "sha3?/std", "strobe-rs?/std", "ripemd?/std", "multihash-derive/std", "core2/std"]