Add memcache functionality and added calls to functions

This speeds compiling my blog up from 3m44s to 37s. That's pretty
significant savings with a few well-placed memoization calls.

The memcache stuff only kicks in for static rendering.
Merge pull request #27 from willkg/memcache

Add memcache functionality and added calls to functions
Speed up tags

Rather than opening the file and unpickling it every time, do it once
and pull it from cache the other times.
Merge pull request #28 from willkg/more-faster

Speed up tags
Reverted tags change due to test fail
Add python versions to classifiers
Merge pull request #30 from willkg/classifier-fixes

Add python versions to classifiers
Fixed both the tests and maru-sama's commit to get AJAX comments working again
Changed the pyblosxom-cmd tests to fail when configured plugins don't load - GH#8