GitLab

Also, our commit messages have been getting better, but we can do
better, and be more consistent. This adds more clarity on how to write
commit messages and provides examples of good and bad messages.

Also, our contributing guide was lacking helpful guidance on how to
start change proposals. This commit adds the start of that section.

Soon, we should add a proposal template to the issue tracker with a link
back to the proposal section, which should also be expanded upon.