Uncommitted things done for issue #56, so aagbsn's patch can be merged with mine.

 * Clean-up previous WIP code
 * move things to TorState
 * improve docs
Add close_circuit method to TorState
Add support for IfUnused flag
unify close_stream, close_circuit and add tests with and without flags on Circuit.close
Fixes for utests to make stream.close() tests which fail
make stream tests pass
Merge branch 'issue-56-resquash' into issue-56-rebase

Conflicts:
	test/test_circuit.py
fix Circuit instantiation after rebase to master