Constants.cs: the CoreImage path has always been wrong on Mac
Fix MonoMac.CFNetwork.dll dependencies. Makes parallellized make work.
Fix crash in macdoc

ScrollToVisible is sometimes called on the previous node, and in some cases this previous node does not have a registered wrapper which causes macdoc to crash. This fix adds a check for the node instead of throwing.
Corrected a dead link.
Merge pull request #115 from MichaelJames6/patch-1

Corrected a dead link.
Merge pull request #114 from spicypixel/hotfix/macdoc-scrolltovisible-crash

Fix crash in macdoc
NSApplication.Init: throw if called more than once
NSTextAttachmentCell: add NSImage ctor, allow instantiating

There were two methods marked [Abstract] which was incorrect.
As such the whole NSTextAttachmentCell class was generated
as abstract, meaning it was only usable if subclassed, which
is not the case in Objective-C. As in Objective-C, the following
is now supported: new NSTextAttachmentCell (new NSImage (...))
maccore: add as a submodule
Makefile: update clean target
Simplify the mac documentation updating
Merge remote-tracking branch 'upstream/master'