The documentation for the `location` property states that "This property contains `nil` if the map view is not currently showing the user location or if the user’s location has not yet been determined." The iOS SDK presently returns a garbage value, which has some rather annoying consequences when the value should logically be nullable. This change should rectify the issue.
With _location no longer initialized to an invalid coordinate, trying to access `_location.coordinate` when `_location == nil` will return `0, 0`, which is a valid coordinate.
- Removes nullability shims for Xcode 6.
- Removes MGLTypes.h from files where it was only being used for
nullability support.
- Accepts that `NS_SWIFT_NAME` is not fully supported by Xcode 7.2 and
lower.
- Adds documentation about Xcode 7.3 requirement.
- Makes the use of apostrophes in the iOS SDK documentation consistent by converting “dumb” `'` into smart `’`.
- Adds ticks around class/property names/values.
- Breaks lines at 80 characters.
