Windows terminal support

[craigfe]

The test suite currently passes on Windows (thanks to #15), but the terminal handling doesn't behave correctly on Windows terminal & Cygwin terminal:

_src_progress.2021-06-29.10-08-43.mp4

Originally posted by @emillon in #15 (comment)

Details about terminal control sequences on Windows can be found here. The fix will probably involve touching Terminal.Ansi, and perhaps also renderer.ml in the Progress library.

[emillon]

to be honest, even opam is a bit broken in windows terminal:

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