Use `Color`, `Intensity` etc. from `ansi-terminal`

[georgefst]

Is there any particular reason why prettyprinter-ansi-terminal redefines its own versions of these types, isomorphic to the ones upstream? I often find myself needing to resolve conflicting imports due to this, especially since the ones from this package are re-exported through pretty-simple.

[georgefst]

Ah, I've just seen this has previously been asked by @sjakobi (no response): #121 (comment).

[sjakobi]

Is there any particular reason why prettyprinter-ansi-terminal redefines its own versions of these types, isomorphic to the ones upstream?

I speculated about this in #224 (comment):

I'm not sure, but I suspect that the local types exist so the internals can be changed with less compatibility hassle. Re-exports also bring their own versioning problems.

Maybe @quchen can comment on the original motivation.

[georgefst]

I'm not sure, but I suspect that the local types exist so the internals can be changed with less compatibility hassle. Re-exports also bring their own versioning problems.

I can't really see either of those having much bearing in practice, particularly given how unlikely the ANSI standard is to change any time soon.