Merge rust-bitcoin/rust-bitcoin#797: Remove Sebastian from maintainers list

42e10ff Only use two newlines before level 2 headings (Tobin Harding)
9be2fb6 Remove Sebastian from maintainers list (Tobin Harding)

Pull request description:

  @sgeisler requested by email to be step down from the position of
  maintainer of `rust-bitcoin`. Remove his name from the contributing document's list of maintainers.

  Implement @dr-orlovsky's suggested [whitespace policy ](rust-bitcoin/rust-bitcoin#795 (comment) we are at it.

ACKs for top commit:
  Kixunil:
    ACK 42e10ff
  dr-orlovsky:
    ACK 42e10ff
  apoelstra:
    utACK 42e10ff

Tree-SHA512: f2e3f3bde5b2e42b0144328dbe4c5c1471764cd5cf0270c71aeee68c4cf962bfc2fd1a5718d4db3809113e5f5a6b92ce0c76582c6d8426a216b025b726fb0e54

Author: apoelstra

CONTRIBUTING.md

@@ -8,7 +8,6 @@ implementation and other Rust Bitcoin-related projects, which are hosted in the
 mostly guidelines, not rules. Use your best judgment, and feel free to propose
 changes to this document in a pull request.
 
-
 #### Table Of Contents
 
 - [General](#general)
@@ -138,7 +137,6 @@ NB: Please keep in mind that the script above replaces `Cargo.lock` file, which
 is necessary to support current MSRV, incompatible with `stable` and newer cargo
 versions.
 
-
 ### Peer review
 
 Anyone may participate in peer review which is expressed by comments in the pull
@@ -147,7 +145,6 @@ test out the patch set and opine on the technical merits of the patch. Please,
 first review PR on the conceptual level before focusing on code style or
 grammar fixes.
 
-
 ### Repository maintainers
 
 Pull request merge requirements:
@@ -162,7 +159,6 @@ Current list of the project maintainers:
 - [Maxim Orlovsky](https://github.com/dr-orlovsky)
 - [Matt Corallo](https://github.com/TheBlueMatt)
 - [Elichai Turkel](https://github.com/elichai)
-- [Sebastian Geisler](https://github.com/sgeisler)
 - [Sanket Kanjalkar](https://github.com/sanket1729)
 - [Martin Habovštiak](https://github.com/Kixunil)
 - [Riccardo Casatta](https://github.com/RCasatta)
@@ -173,7 +169,6 @@ Current list of the project maintainers:
 
 Library reflects Bitcoin Core approach whenever possible.
 
-
 ### Formatting
 
 The repository currently does not use `rustfmt`.
@@ -189,14 +184,12 @@ and [how it is planned to coordinate it with crate refactoring](https://github.c
 For the new code it is recommended to follow style of the existing codebase and
 avoid any end-line space characters.
 
-
 ### MSRV
 
 The Minimal Supported Rust Version (MSRV) is 1.29; it is enforced by our CI.
 Later we plan to increase MSRV to support Rust 2018 and you are welcome to check
 the [tracking issue](https://github.com/rust-bitcoin/rust-bitcoin/issues/510).
 
-
 ### Naming conventions
 
 Naming of data structures/enums and their fields/variants must follow names used
@@ -205,7 +198,6 @@ in Bitcoin Core, with the following exceptions:
   snake_case for fields and variants);
 - omit `C`-prefixes.
 
-
 ### Unsafe code
 
 Use of `unsafe` code is prohibited unless there is a unanimous decision among