Release charmstore-client 2.2.0

New & noteable in this release:

Add term publishing plugin commands to whitelist.
Add support for new charm store channels: stable, candidate, beta and edge.
The development channel has been replaced with edge.
Rename publish subcommand. It is now called "charm release" to be more in line
with snappy semantics.

Other improvements:

Add bash completion.
Generate man pages.
Cache plugin help.
Use a whitelist and call charm-tools-commands to extend the whitelist.
Change push resource to attach, --resource option.