#19 Add Mac support

[Nate B.]

STIRHS should be redesigned to be able to work on both Mac OS X and
Windows.

Porting STIRHS onto the Mac platform will allow one of the developers
(nate_broussard) to easily work on the code. GUI-related features on
the Mac will probably remain significantly behind the Windows
developments, and we will attempt to keep the Windows version from
becoming bogged down by adding Mac compatibility.