scripter2: Explicitly include Python.h in all files.

This silences warnings that show up when Python.h is not included first.
There was a workaround in one place, but it did not extend to all uses,
and it didn't work in all cases.
scripter2: Fix type conversion warnings.
Add notes about using Python 3.
Swap order of Python initialization.

See https://groups.google.com/forum/#!topic/vim_dev/5MYb23t9ZBM
Stop calling PyEval_ReleaseLock.

It is not necessary: http://stackoverflow.com/a/14925010
Use new-style exception handling.
Use print function.
Merge pull request #1 from QuLogic/master

Python 3 support