Custom highlight range color support

[bojan88]

Implements #1699, and related to #339

Basically, adds support for css hex color in line range - i.e. 30:40#ff0.

Please take this PR with a grain of salt. Note that it might not be going in the right direction that maintainers would like. I started working on #1699, and the change grew substantially, but then I saw that #339 is the preferred way to solve the issue.

This is just my idea how we could implement this, and maybe a place for further discussion. Please feel free to request changes or even completely discard this PR if you think this is not the way bat should evolve.

[bojan88]

There was a strange error from cargo check --locked --target=x86_64-unknown-linux-gnu --verbose --lib --no-default-features --features regex-onig that LineRange was not in scope even thou there's use crate::line_range::LineRange; at the start of the file

[sharkdp]

Interesting idea. Thank you for your contribution. The proposed format looks a bit strange at first, but it really adds a lot of flexibility. And I think it would be compatible with the format in #1841 as well?

What do the other maintainers think? @eth-p @keith-hall @Enselic?

[Enselic]

Thanks for taking the time to make a contribution @bojan88.

Like you realized yourself, doing something more generic in line with #339 would be better, I think.

I'm not sure it is a good idea to go ahead further with this PR, TBH. Doing so would make #339 harder to implement (because then you have to take compatibility with this into account), and #339 is still something that would be great to have.

[bojan88]

Sounds good. Feel free to close this anytime.
Or let me know if you want me to update it in case you think something similar might work.

[Enselic]

Thank you for your understanding. Let's close this for now then.