Respect the Auto/Rate/Seeking

- Treat HwaMode(-1) as Auto instead of Unset
- Treat HwaResolution(-1) as Auto instead of Unset
- Add methods to modify rate (untested)
- Add method to allow for relative seeking (untested)
- Add check to ensure that we don't try to seek to a negative absolution
position
Merge pull request #91 from babgvant/master

Respect the Auto/Rate/Seeking