RDoc color scheme

[colby-swandale]

I think it's time to take a look at having something more friendly and accessible to the eyes. Let's use this ticket to capture some ideas and see if we can break some ground on putting a new set of colors together for RDoc.

Long live the green!

[st0012]

We're also improving RDoc's development process (e.g. #1151). But before that's merged, you can use these steps to generate the documentation and see the changes:

1. Run bundle install
2. Run bundle exec rake
3. Run bundle exec rdoc or bundle exec rake rdoc to generate the documentation