Ability to nest styles

[seaneagan]

Currently when you try to nest styles it doesn't work because when a pen is done writing it resets all styles, not just its own. Here's one take on an API to do this:

https://github.com/sindresorhus/chalk#api

[jtmcdole]

I know I'm late on responding to these. I like the idea of storing a stack of "complete state" such that:

1. down: bold + red + green background
2. down: bold + blue background
3. up

Would see only having the blue background removed and green background restored at step-3