Pass style as argument to be able to calculate it at runtime

From https://github.com/LukasKalbertodt/bunt/issues/1#issuecomment-812863115:

> Could the color and other styles be specified by argument? For example,
> 
> ```rust
> bunt::println!("{$*}error:{/$}", Color::Red, ty);
> ```
> 
> In that case I could calculate the color at runtime.