Refactor macros [Work in progress]

* Move old macros to DDLegacy which by default is imported when CocoaLumberjack.h is not used. Makes the library 1.9.x backwards-compatible.

* Redefine 2.x.x macros in DDLogMacros. Everything can still be redefined/improved here without worrying about backwards compatibility.

To do:

- [x] Update demos.
- [x] Update framework/static library.
if we change async from a macro to YES/NO, I think we are loosing the mechanism for easy changing them, right?