ANSI escape sequence handling improvement

[dra27]

Gcc's error messages use some ANSI escape sequences which confuse AppVeyor's colouring.

Broken example: https://ci.appveyor.com/project/dra27/ocaml/build/1.0.130#L4639
Work-around example: https://ci.appveyor.com/project/dra27/ocaml/build/1.0.129#L4639

I'm running the script with TERM=ansi and then post-processing the output with sed. It'd be lovely if you were able to address these three shortcomings of AppVeyor's ANSI processing:

1. For ESC[K (and other unimplemented sequences) would it be possible for AppVeyor just to omit displaying the sequence?
2. ESC[m should be treated as ESC[0m (ECMA-48 8.3.117)
3. In the parameters for m, 01 should be treated as 1 - i.e. ESC[01m is a bold instruction and ESC[01;31m is a bold+red instruction - this gets mis-translated in the resulting HTML output (ECMA-48 5.4.2 f)