Follow Blogs: Remove unused $bp global in get_button() method.
Follow Blogs: Add phpDoc for rss_handler() method.
Merge branch 'master' of github.com:r-a-y/buddypress-followers
Cache follow counts.

This commit:
- Caches calls to BP_Follow::get_counts().
- Removes redundant calls to bp_follow_total_follow_counts().  Fixes #36.
- Invalidates count cache when a follow relationship is saved / deleted.

More caching to come!

See #36.