Fixed incorrectly decoded mfg and product strings.

Signed-off-by: Chris Reed <flit@me.com>
Made VID and PID params optional on enumerate().

Signed-off-by: Chris Reed <flit@me.com>
Releasing GIL during USB I/O operations.

- The GIL is now released during read(), write(), get_feature_report(),
  and set_feature_report().

Signed-off-by: Chris Reed <flit@me.com>
Merge pull request #6 from flit/master

Bug fix and releasing GIL during I/O