Support mintty under Windows

[Zapeth]

Is your feature request related to a problem? Please describe.
terminal::size() reports incorrect terminal dimensions (80, 25 - the default Windows cmd dimensions) when launching from a mintty instance, presumably because crossterm/src/terminal/sys/windows.rs only uses native Console api functions?

Other commands/features might also be affected, I haven't done extensive tests (though at least basic commands like coloring and cursor positioning seem to work properly).

Describe the solution you'd like
The code in crossterm/src/terminal/sys/windows.rs should include checks/code for non-native Windows consoles where necessary in order to ensure proper results when using such terminals.

Additional context
I put this as a feature request since mintty wasn't listed under the "Tested Terminals" list.

edit: Just noticed that non-ascii characters are also not properly displayed in mintty, example tästÜng croßter€ displays tästÜng croßter€ (is displayed correctly in cmd/Powershell)

[TimonPost]

see: #580