Add some more P/Invokes to libgpod functionality.
Add some more P/Invokes to libgpod functionality.

Signed-off-by: Nathaniel McCallum <69bc4957b0eae5f77fa6131eb01ae14712c4b615@natemccallum.com>

hyperair/libgpod,hyperair/libgpod,hyperair/libgpod,hyperair/libgpod,neuschaefer/libgpod,neuschaefer/libgpod,neuschaefer/libgpod,hyperair/libgpod,neuschaefer/libgpod,neuschaefer/libgpod