Add `instance {Bits,FiniteBits} Bool`

This interprets `Bool` as an 1-bit "unsigned" bit-field and provides a
simple (not particularily optimized) implementation to that end.

See "Proposal: Add `instance Bits Bool`" by @ekmett, Nov 2013,

 http://permalink.gmane.org/gmane.comp.lang.haskell.libraries/20663

Signed-off-by: Herbert Valerio Riedel <hvr@gnu.org>