Merge pull request #9 from handyman5/feature/directory_pages

Support for directories and page crumbs
Merge pull request #11 from handyman5/bugfix/git_history_merges

Adding "--no-merges" to git log to fix _history
Added caching support to wiki.index()

Rather than recalculating the index every time we load a
directory listing or ask for tags, cache it for a while.
Also invalidates the cache for that directory when a change
is saved there.