First go at DiskCache. Unit tests pending.
Make cachePath and cacheQueue lazy
Remove semicolons
Add default values for convenience
Further DiskCache unit tests and fixes

Had forgotten to make sure the directory is created
UIImage extension unit tests
Add TODO
Rename cache -> memoryCache
Rename MemoryCache -> Cache

The Cache class is both a memory and disk cache. In fact, the “memory
cache” is NSCache.
Add unit test for empty name
Merge pull request #21 from hpique/feature/disk-cache/save-image

Save image in disk cache. Closes #5.