feat: add colored attributes

[joris-bright]

Closes #61

Adds support for coloring attributes (incuding level, time, msg, source)

[lmittmann]

Thank you for the effort! I like the idea of ColorAttr and its flexibility to be used for special attributes, like level, as well as "normal" attributes. Also the fact that it can respect the NoColor option is great.

There are a few question that remain: Can this be achieved with less allocs (the amount of allocations doubles with this implementation)? Is there a more flexible way to handle colors (maybe also support 256bit colors)?

The idea is great! I think it might need a bit of iteration implementation wise.

[joris-bright]

@lmittmann I'll have a look if I can improve it 👍

[joris-bright]

Number of allocations should be better now. I've also updated the implementation of Color.

[lmittmann]

This will be added in some form, I just have currently no time to work on it. Sorry for the delay.