Provide pkgconfig file (#68)

Provide a pkgconfig file that is configured in a similar
manner to the cmake config file. It doesn't yet have all the
logic for different platforms and hasn't been tested.
Remove rpath from pkgconfig
Config multiplatform support in cmake and pass to pkgconfig
Merge branch 'master' into issue_68

Conflicts:
	CMakeLists.txt
Remove rpath from SimbodyConfig.cmake (#113)
Merge pull request #114 from scpeters/issue_68

Provide pkgconfig file (#68) and remove rpath from SimbodyConfig.cmake (#113)