Release 2.2

Here's a minor release.

-----

### Bug Fixes

* Fixed using the numpad to commit candidates. (Mathieu)

### Docs Improvements

* Added installation instructions for Arch Linux. (Antony)
* Removed an obsolete (and confusing) notice about release tarballs. (Mathieu)

### Testing improvements

* Get Travis CI to build against the 1.x branch of libcangjie and pycangjie, as
  their master branch has now broken the API in a way that ibus-cangjie 1.x
  doesn't build against it any more. (Mathieu)
* Use the in-memory GSettings backend for the tests, so avoid any undesired
  side-effects from the running environment. (Mathieu)