Python inline with modules

[ntyunyayev]

Addressing #95 with @cdelzotti.

• Added --python-inline cmd argument to enable legacy behaviour that interprets text inside $(( )) as a Python expression. This feature is now disabled by default.
• Can be added per section using a new python-inline option, similarly to the existing "jinja" keyword
• Added python-inline options in modules when necessary

This is a draft of the implementation and requires more testing before merging