implement direct pin for beaglebone

Signed-off-by: Travis Berry <contact@travisberry.com>
Merge pull request #72 from ninetwentyfour/dev

implement direct pin for beaglebone
Ensure slots are not already written into the capemanager

Ref PR https://github.com/hybridgroup/gobot-beaglebone/pull/4

Conflicts:
	platforms/beaglebone/beaglebone_adaptor.go
Write to pwm pin when its ready
Merge branch 'dev'