Fix createWroter.

Fixes https://github.com/jdf/Processing.py-Bugs/issues/99
Build 0366.
Fix PVector.dot instance ethod.

Fixes https://github.com/jdf/Processing.py-Bugs/issues/101
Build 0367.
add support for multiple-arg PVector .add()/.sub()
Merge pull request #111 from aparrish/more_pvector_fixes

add support for multiple-arg PVector .add()/.sub()
Do PVector.add in Python to save some garbage.
Do PVector.sub in Python to save some garbage.
Implement PVector.lerp.

Fixes https://github.com/jdf/Processing.py-Bugs/issues/102
Build 0368.
Sketching out mode-detection.