Update podspec to 2.3.0-beta.4

Bump podspec to 2.3.0-beta.3

Disable deprecation warning inside the library

Disable deprecation warning inside the library

Prefix import functions with MR_ to avoid conflicts

Closes magicalpanda#722.

Fix for magicalpanda#387

Improved error handling

- Let’s handle an addPersistentStoreWithType:configuration:URL:options:error: error regardless of whether we want to delete the store on model mismatch.

More robust deletion of SQLite stores

- Core Data makes other supplementary files in addition to the .sqlite file, so deleting those as well for good measure.
- Previously, we had this Core Data deletion implementation in our app code and then MagicalRecord used another Core Data deletion implementation.  It’s best if everyone can use one Core Data deletion implementation.  As a result, making this a public method on NSPersistentStore so that everyone has access to it.

Better logging story

- MagicalRecord now correctly detects CocoaLumberjack.
- Updated MagicalRecord to use different log levels when
CocoaLumberjack is available.  When CocoaLumberjack is not available,
all log levels are logged via NSLog when DEBUG is defined and not
logged at all when DEBUG is undefined.
- Since MR_ENABLE_ACTIVE_RECORD_LOGGING doesn't easily work with
CocoaPods and because CocoaLumberjack is a better solution, I've
removed MR_ENABLE_ACTIVE_RECORD_LOGGING entirely.