Do not try to install windows-curses in MSYS2

[dobairoland]

@ulfalizer Please take a look. I believe that this solves the problem.

Closes #77

[ulfalizer]

Won't work when Kconfiglib is installed as a Python wheel, unfortunately. Wheels are the usual case nowadays, e.g. when using pip.

setup.py only gets run when building the wheel, not at installation time.

Thinking I should just drop the windows-curses dependency, bump the major version, add a warning somewhere, and hope it doesn't cause too many problems. Would be nice if there was some hacky way to detect MSYS2 with the Wheel format though.

[ulfalizer]

Fixed a different way with 068bc48.