Clean up a few imports and rename two ARC specs
Adds support for checking if a file URL exists

expect(URL).to(exist);
// or
cacheURL should exist;
Adds support for checking if a file path exists (as an NSString *)

expect(path).to(exist);
// or
path should exist;
Create caches directory if it does not exist

This is needed when we run iOS specs outside of the simulator, for
instance in Travis CI or via rake
Merge pull request #152 from akitchen/ExistMatcher

Adds a matcher to check if a file URL/path exist