Supporting NSMapTable

Much of the same implementation as NSDictionary and NSMutableDictionary
Making the headerfile public for mac framework
Merge pull request #272 from hfossli/nsmaptable

Supporting NSMapTable
Block execution cleanup, type-safe headers, use QOS
Slight macro cleanup
Move to XCTest async testing
Rebuild Xcode project, iOS framework, module love, use xcconfig
Universally move to module imports
Remove deprecated NSURLConnection forwarding
Use Core Foundation block-based timer
Fix test failures from iOS 8 workaround
Control events don't work without an event loop in iOS 8
MFMail attempts to use nil in a dictionary without event loop in iOS 8
Clarify bk_removeEventHandlersForControlEvents. Closes #265.
Loosen type compat. for Swift being a lying liar who lies. Closes #260.
Use instancetype, other modern syntax. Closes #229.