Script to format app code

[aalin]

It would be useful to have a script that formats the application code.

These libraries are already included in the gemspec and support formatting:

• ruby-syntax-tree/syntax_tree
• ruby-syntax-tree/syntax_tree-haml

What's missing is a CSS formatter, I don't know how difficult it would be to write one.

The idea is to run bin/mayu format in the project root and it would format all the files.