* Create howto.tid
Howto explains customising the languages supported by the highlight plugin. This involves:
* Using the highlight.js download page to get a zip archive containing the files for a highlight.js server which supports a set of languages selected by the user
* Replacing the highlight plugin's `highlight.pack.js` file with the `highlight.pack.js` file from the downloaded archive
* Update plugin.info
Add howto.
