Fancy configurable prompts!

* Prompts are now generated based off of string templates,
  for example: "%(bold)sT:%(extruder_temp_fancy)s %(progress_fancy)s
  >%(normal)s "

* We have a dictionary of prompt string templates for different
  situations.

* We have bold support for the prompt.

* We have extruder temperature support for the prompt.

* We have progress support for the prompt.
Merge pull request #319 from colah/dynamic-prompt

Fancy configurable prompts!