More Color Support

[quininer]

Windows 10 already supports 24bit colors. We can use VT mode first, and fallback to wincon if it is not available.

https://blogs.msdn.microsoft.com/commandline/2016/09/22/24-bit-color-in-the-windows-console/
https://docs.microsoft.com/en-us/windows/console/console-virtual-terminal-sequences

https://github.com/BurntSushi/termcolor/blob/master/src/lib.rs#L497
https://github.com/ogham/rust-ansi-term/blob/master/src/windows.rs#L10

[murarth]

I'm willing to support this, but I don't currently have a way of testing it. My system (Debian 9 stable)'s version of ncurses contains no terminfo setting for true color (although gnome-terminal does indicate xterm-256color as its TERM setting). And wineconsole does not appear to support terminal escape codes.

I've pushed a branch, true-color, with a basic implementation (for Unix only). If you wanted to build on top of that and submit a PR, I would be open to accepting it.