ColorCodes: simplify and comment a bit.

- Simplify logic and increase explanation to make it easier
  for the casual reader.
- Remove the undocumented, untested and not-clearly-working
  "percentage" support.
- Replace `eval` with `try`, as is my wont.

Addresses #620.
Is there any easy/pretty way of using `&nbsp` to prevent the text from wrapping mid color-code like this:
![rgb__100_100_100__at_duckduckgo](https://cloud.githubusercontent.com/assets/873785/4209874/b63ee4da-386e-11e4-93e9-392c73881b52.png)