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.