Disable colors on Windows, enable if --colors is used

[jarun]

Windows does not support POSIX colors by default. It works on terminals like ConEmu.

The plan is to disable colors IF the detected platform in Windows (same as --nc effect).
Enable colors only if option --colors is used.

The relevant discussion is here.

[dertuxmalwieder]

I'd still recommend to - at least - check for ConEmu first, e.g. via the env. variables.

[jarun]

No problem. I have reviewed the change. Please take a look.

[jarun]

Note: someone might come back someday asking to support another Windows terminal emulator like ConEmu. It would still work for them if ConemuDir is set as an env var.

[dertuxmalwieder]

It should be trivial to support any "working" ConEmu-like thing (like console² - someone should test that... ;-)) or non-cmd shells as long as they come with their own environment variables. I guess the only reason not to just add a whole bunch of supported cases would be the code size.