Creation of colored strings should probably be `const fn`

[PvdBerg1998]

See title. I don't know if this is already possible using the current possibilities of const fn, but setting a color on a constant string is definitely something I would expect to be possible.

[mackwic]

That's a great idea ! Would you like to try a PR ? I currently does not have time to work on it.

[maxrumsey]

I'd be happy to take a stab at this, if no one else is planning on doing it!

[kurtlawrence]

@maxrumsey Please do =)

[sameer]

I tried to do this, and it's a lot more complex than I thought it would be. You can't use Strings in const fns so it needs to be a separate struct with a &str and a bunch of const fns for coloring + styling.