TST/API: Actually test single-node storage; add default key
ENH/PERF: Added storage class with frame number cache.
BUG: Storage class __del__ if file open failed
BUG: Storage put() failed if no index <= 0.
BUG/ENH: Fixed pytables __del__ crash, added context methods
BLD: Added pytables dependency
TST: Skip Pandas HDFStore if no pytables

(I have verified this works in a pytables-free env)
ENH: **kwargs to storage classes, for compression etc.
Merge pull request #100 from nkeim/storage_cache

Storage class with frame index cacheing