Adjust indentation and spacing in tests.js
Add memcache cache provider

Add a new cache provider using memcache (the `memcaching` npm module).
The cache provider takes an `MemcacheClient` as input, and then uses that
client to cache `InResponseTo` validation checks, etc.

Unit tests have been updated to check both the `MemcacheCacheProvider`, and the
default `InMemoryCacheProvider`.
Merge pull request #6 from Asana/add-memcache-provider

Add memcache provider