Fix swallowing of PickleError in FileSystemCache

Oh yeah and with-statements are now allowed. \o/
Added success return values for MemcachedCaches.
Added success return values for RedisCache.
Added success return values for FileSystemCache.
Cache write statuses for default implementations.
Some smaller things i missed.
Add more tests
Catch PickleError
Merge branch 'filesystemcache' into cache_write_statuses
Add API specs
WIP conform to definition in module docstring
Bugfixes

WAS BORN A TECH WRITER
REVOKE COMMIT PRIVS
And another one
New rules
Rewrite testsuite WIP
Clear up some duplicates
Strings...
Add changelog entry
Better docstrings
Fixed a broken example.  This fixes #419