iOS Support

Ported to iOS. Seems to work. #87 

iOS doesn't implement `NSComparisonMethods` protocol since the one was made for MacOSX's scripting support. iOS doesn't deal with scripts. 

Those methods, leaving scripting behind, are identical to the usual `compare:` and `isEqual:`.

Also had to change a class of `weight` property of `EKEdge` from `NSObject` to `NSNumber`. Why `NSObject` in the first place?

Made preprocessor's statements around imports in addition to ones in `.h` and `.m` files of iOS-only categories to protect them from IDE's import optimisations and suppression of warnings.