Auto-generate Ratchicons

- [x] Work around whitespaces in `<pre>` (https://github.com/jekyll/jekyll/issues/1801)
- [x] Add a proper license header to ratchicons-data-generator.js (suggestions welcome, since this isn't consistent ref #419 )

~~Find a way to show the title for each Ratchicon without adding it in `<pre>` code /CC @connors~~