Moved from Byte to Boolean in Garbled Circuits

The API confused me when I saw Bytes being passed around.
It's only Booleans, no?  If so, we better be semantically correct and
use Booleans.
This modifications compiles, but I don't know whether anything broke.

I guess a few iterations need to be made until this is a perfect patch.
For example, the boolsToBytes could probably be moved to a more central place.
Documentation probably also needs to be updated, but I haven't checked.