Added count() method to SugarRecordObjectProtocol so it can be called directly from an object type (e.g., SomeObjectClass.count()), rather than via all().count().
Optimized core data implementation of count() to use `NSManagedObjectContext.countForFetchRequest()` instead of loading all instances of the object into memory and counting them.
allow count to work when a predicate is passed to limit the results
Merge pull request #87 from twobitlabs/add-count

Add count() method to entities and optimize Core Data implementation