Update batcache with latest version from Automattic

Latest as of https://github.com/Automattic/batcache/commit/3099b48f44b481b5953402747f4913638e8555ab
Remove unused batcache_stats() functionality

No need for the overhead
Bump version number on Batcache advanced
Merge pull request #158 from washingtonstateuniversity/batcache

[PR] Update Batcache