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.
Expose the text() method that renders ints.

Fixes https://github.com/jdf/Processing.py-Bugs/issues/105
Build 0369.
Better detection of sketch mode (active/static/mixed), with a (possibly)
more helpful error message on detection of mixed mode.

Fixes https://github.com/jdf/Processing.py-Bugs/issues/95
Build 0370.
Fix typo in MixedModeError message.
Attempt to call registered dispose handlers on uncaught exceptions.

Fixes https://github.com/jdf/Processing.py-Bugs/issues/97
Build 0371.
Don't indent on return if the cursor is positioned at left of program text.

Fixed https://github.com/jdf/Processing.py-Bugs/issues/81
Build 0372.
Permit the use of hand-rolled or single-jar libraries in Python Mode.

Fixes https://github.com/jdf/Processing.py-Bugs/issues/98
Build 0373.