Contributor guidelines

Formatting git commit messages

See this post by Tim Pope. Vim with syntax highlighting on attempts to enforce this format, which is nice because it'll alert you if your commit message is too long etc.

Tabs vs spaces

Yes, spaces are better, but tabs are used pretty much everywhere in this project, for mostly silly reasons. 2 spaces are used for indentation in _plugins/slugify.rb because that's the convention in Ruby. (Tabs are used in _plugins/blocks.rb for some reason. Not sure how this happened or whether or not it's worth changing.)