prettyprint should have option for light terminal

[TedDriggs]

On macOS, the default terminal is black text on a white background (and since I have difficulty seeing red-on-black, I prefer to keep it that way). As a result, when cargo-expand uses prettyprint, certain syntax elements become invisible white-on-white text that renders the output unusable.

Options

1. Somehow detect the terminal background color and choose a contrasting color for primary text. Doing this in a cross-platform way might be difficult.
2. Add an option for callers to tell prettyprint to use a light theme vs a dark theme. This would require cargo-expand and others to expose a command-line flag of their own to choose light vs dark, but it would avoid reading anything from the terminal.

[mre]

This can be done already. Prettyprint supports all colorschemes that syntect supports. So it might be as easy as sending a pull request to cargo-expand (or cargo-inspect, which is also using prettyprint) and add the flag as well as choose a colorscheme.

[mre]

And yes I agree, the screenshot looks quite awful. 😀

[mre]

This is now done in cargo-inspect thanks to @jonathansty.
See the release notes here.
It uses prettyprint 0.4.0, which has support for the get_themes method. See here.

I think we can close this. 🎉

[mre]