Fixes #4

Fixes #3, which was a misdiagnosis.

* More inline documentation
* Actually purges when requested
* Better error handling

Closes #1

Also adds a bit of missing inline documentation.

Fixes #1.

See #1.

Handle Ajax-based requests to purge a given post's revisions. Fully functional, though some UI work is needed.

See #1.

See #1.

See #1.

Don't register hooks immediately when plugin is instantiated, otherwise no one else can hook in reliably.

Remove unnecessary use of array_unique. Post types are stored internally using the type slug as an index, so there can't be duplicates to begin with.