Replace Specta specs with XCTestCase
Latest Expecta
Silly Git
Derpy Git
Add a contribution guide based on GitHub's used in the ReactiveCocoa project
Remove requirement to defined MR_LOGGING_ENABLED before logging works.

Use `MagicalRecordLogLevelOff` to disable logs.
Disable logging during tests
Deprecate `MR_createInContext:` in favour of the more consistent `MR_createEntityInContext:`, and similarly for `MR_deleteInContext`
Disable deprecation warning inside the library