Close #1930 Convenience methods for zlib

Close #1930 Convenience methods for zlib

This is a combination of 20 commits. Their commit messages are preserved
below for the benefit of future generations.

* Adding a shortcut to easily compress/decompress a string of text.
* Making the API consistent. unzip should accept a Buffer for input as well.
* Adding docs.
* Oops, typo.
* Propagate error through the callback.
* Adding zlib from string tests.
* Typo in test.
* Remove 'end' listeners, and join buffers properly instead of joining them
  as a string.
* Oops, needs to be rendered to a string.
* Updated test to include multi-byte characters.
* unzip should return a raw Buffer. Updated docs to reflect.
* And finally updating test.
* EventEmitter.destroy() is a bit more customary
* Revert "EventEmitter.destroy() is a bit more customary"
* Renaming internal methods to "buffer" instead of string.
* Remove the 'error' listeners as well.
* @isaacs: spacing/style, and compress duplicate functions into one
* @isaacs: Update docs
* @isaacs: doc style fix