Adding initial OS X 10.10 Yosemite Support.

Note!
Converted NSWindowMask constants to enumeration.
The Apple documentation names these 'enum', and I found these more convenient to group together this way, it may break some code if people used the constants directly, but existing methods and properties do most of the NSWindowMask manipulation already. 
Let me know if it's alright to keep them this way or if they should be restored.