Fix Game Kit blocks that reference UIImage.

Previously mappings.xml was used to convert these erroneous handlers by changing UIImage to NSImage. This can't be done in mappings.xml which is used by iOS as well.
Add support for parsing enum formats with comments containing the type.

For example:

typedef enum /*: NSInteger */ {
   GKGameCenterViewControllerStateDefault = -1,
   GKGameCenterViewControllerStateLeaderboards,
   GKGameCenterViewControllerStateAchievements,
   GKGameCenterViewControllerStateChallenges,
} GKGameCenterViewControllerState;
Update availability.
Update generator to handle OS X DocSet v419.33.
Merge branch 'hotfix/mapping-uiimage' of https://github.com/spicypixel/monobjc-tools into spicypixel-hotfix/mapping-uiimage
Remove definitions.
Merge branch 'hotfix/enum-parse-type-comments' of https://github.com/spicypixel/monobjc-tools into spicypixel-hotfix/enum-parse-type-comments
Add missing GameKit files.