Enable colored output on Windows

Enables 16 color terminal support if `terminfo` isn't supported and one of the following conditions is met:

* The environment variable TERM is NOT definied, but `libc::isatty` returns something >0 (e.g. cmd.exe).
* The environment variable TERM is "cygwin" (e.g. msys terminal).
* The environment variable TERM starts with "xterm" (e.g. cygwin's mintty terminal).

Fixes #2807 except for attributes other than ForegroundColor and BackgroundColor.