temp hack: Skip baudrate test on OS X

OS X doesn't support the same method for changning serial speed as
Linux does. Until I have time to look into the right way to do this,
we'll just skip this test for now.
Update MBus `b' message to always send 4 bytes
Merge branch 'master' of github.com:ppannuto/M-ulator
Update v0.2 GPIO support

I'm not 100% on this, but should be enough to get Ben going