Improve the Python to C++ conversion tool

Desirable

• Other language constructs?
• Preserve comments (see license fiddling in test). They are apparently not represented in the AST?

Pending

• Test suite

Done

• Unary operators (+=) (augmented ops)
• index expressions [], slices s[1:2]
• Default values of function arguments still broken
• "->", "." depending whether variable is on stack (from function def)
• Missing newlines around some expressions
• Some smartness regarding Qt classes passed as function parameters
• Handle type annotations
• Context mgrs
• Type annotations around funcs
• Some smartness regarding Qt class construction
• Operators
• Return statements