A bunch of new MySQL global status tracking plugins.

This commit adds 6 new MySQL plugins that track a number of additional
values that MySQL reports in global status.

Buffer pool stats: tracks operations on the buffer pool, as well as its
                   current size.
Data/Log stats: Tracks data & log operations (reads, writes, bytes
                read/written, etc)
Extra stats: Miscellaneous stats
Handler stats: Tracks operations on MySQL's handler layer
Innodb rows stats: Stats about InnoDB's operations at a row level
Sort/Select: Tracks sort & select type counts