Add option to exclude huge files

[pyhedgehog]

Background

Sometimes repositories contains source files too big to be parsed by pygount (I've stuck with 40Mb text file that seems to be source for ML-model). I propose simplest solution — option exclude huge files from processing.

Goals

• When option --larger-to-skip is passed, every file that is larger than specified size is skipped from parsing.
• Support parsing size specifiers like 10k, 20m and so on. Maybe borrow code from test.support._parse_memlimit()...

[roskakori]

Yes, this makes sense.

Not a high priority, but I will probably work on pygount during the coming holidays, so we will see.

Actually, in analysis.py you can already find this in SourceState:

    generated = 6
    # TODO: 'huge' = auto()  # source code exceeds size limit
    #: pygments does not offer any lexer to analyze the source
    unknown = 7