Minor updates to documentation
Relocated platform specific includes so they are only included in the headers. Since this is technically an API change that might theoretically change calling code if it was poorly designed enough to really on this undocumented inclusion of windows.h or unistd.h it will have to change to do that itself.
Fix warnings when extra includes are involved.
Now datatypes.h and crossplatformexport.h are replaced by those in the Mezzanine and every other file is simply copied into Threading.