Also minor changes:
- Remove unused headers.
- rename SimpleExprParseState -> ExprParseState
- rename max_ops -> ops_count_alloc
Was misleading since maximums are often limits which can't be exceeded.
Simple isn't a good prefix for library names since
lots of unrelated modules could be called 'simple'.
Include 'py' in module name since this is a subset of Python,
one of the main motivations for this is to be Python like/compatible.
