Updated for QGIS 2.0

- Updated to new PyQt string API
- Added check for invalid provider field default
Cleanup code and bring inline with PEP 8 style
Switch to new-style PyQt connections and clean up some redundant code
Increase tolerance resolution to 3 decimal places (for sub-meter map scales)
Add ability to halt drag-drawing with a secondary click

- Ensure QgsRubberBand is deleted if secondary click happens during drag-drawing
Update metadata with changes and bump to 0.3.0
Merge pull request #1 from dakcarto/update-for-2.0

Update for 2.0