Add missing includes for integer type definitions.
Add libopencm3 as a submodule.
Add local libopencm3 to include and library path.
Add libswiftnav as a submodule.
Detect Windows and ask cmake to generate MSYS makefiles for libswiftnav.
Updated libswiftnav.
Merge pull request #5 from gsmcmullin/submodules

Include libopencm3 and libswiftnav as submodules.