Bugfixes

[gaya-]

Hey,

We used your driver in our teaching project and found some bugs.
I can't make a PR because the commits to make your software work on our robots are mixed with bugfixing commits.
So, here's just a list of commits that you might want to cherry-pick:

8c4513d
8d4054e
0a95f8b

The last commit also includes a possibility to invert the motors, in case they are wired differently. It's an extra feature but it also includes a bugfix. The line 0a95f8b#diff-c00ddbd0620c770bb87191dbe474030cL231 is wrong, you can't use if enc1 in locals() to check if a variable has value. So if you don't want the feature I would at least get rid of this line.

Cheers and thanks for providing this!
Gaya

[doisyg]

Is it possible to integrate these commits, that would be really useful!

[sonyccd]

Please make a pull request