Add the ability to define custom levels.

[jeffreydwalter]

Hey Sean,

Great work on this logging library! It would be made even more awesome if there was an easy way to override/define custom logging levels and colors.

Just in case I missed something, is this something that can be done currently?

[seanmonstar]

It doesn't exist yet. I can see this being helpful. I'll add this to the 1.0 milestone.