Refactor the code to use http-client

This also refactors the codebase to work on a custom 'ZulipM' monad
transformer, rather than the IO monad. I still need to fix-up the
documentation and clean this up a bit, but this will make implementing
the rest of the API calls - including #5 trivial.
Add missing API endpoints and refactor

This fixes bugs and adds a bunch of missing endpoints, including
removing subscriptions (#5).
Add unit-tests for some of the functions

Also, stub the Zulip API server so our tests aren't actually making
requests to a live server.
Fix haddock module header on `Web.HZulip`

I'd copy and pasted it from `butter-core`. Oops?
Update the README to reflect the new interface

This updates the repository's example and adds a note on the
outdatedness of the currently implemented bots.
Improve and fix-up the haddock documentation

Fixes broken links and removes unnecessary notes.
Bump version to 1.0.0.0