Add option for uncolored compiler output

[pttydou]

Fixes #55.

This adds -nc/--no-color and applies it to compiler diagnostics. The test runner now disables ANSI output, so stderr fixtures are plain text.

Tests:

• python -m pytest test.py -k 'compile_if3 or proc_tc' -q
• python -m py_compile config.py state.py cont.py parsing/parsing.py type_checking/type_checking.py test.py

I couldn't run the full fasm/wasm suite locally because fasm and wabt aren't installed on this Windows host.

[farkon00]

Changes look good to me. Thanks for contributing!