Add Zopfli to Compression

Surprised that this wasn't already on here. I've been using this for native Gzip compression since it released last year.

README.md

@@ -401,6 +401,8 @@ See also [http://areweideyet.com/](http://areweideyet.com/) and [Rust and IDEs](
   * [dropbox/rust-brotli](https://github.com/dropbox/rust-brotli) — Brotli decompressor in Rust that optionally avoids the stdlib
 * bzip2
   * [alexcrichton/bzip2-rs](https://github.com/alexcrichton/bzip2-rs) — [libbz2](http://www.bzip.org) bindings [<img src="https://travis-ci.org/alexcrichton/bzip2-rs.svg?branch=master">](https://travis-ci.org/alexcrichton/bzip2-rs)
+* gzip
+  * [carols10cents/zopfli](https://github.com/carols10cents/zopfli) - implementation of the [Zopfli](https://github.com/google/zopfli) compression algorithm for higher quality deflate or zlib compression
 * miniz
   * [alexcrichton/flate2-rs](https://github.com/alexcrichton/flate2-rs) — [miniz](https://code.google.com/p/miniz/) bindings [<img src="https://travis-ci.org/alexcrichton/flate2-rs.svg?branch=master">](https://travis-ci.org/alexcrichton/flate2-rs)
 * snappy