New pdf.js checklist
---------------------
*  Pull newest version
*  Build pdf.js with `node make generic`
*  Copy pdj.js/build/generic/ into pdf.js-[old short hash]
*  Get new short hash with `git log abbrev-commit`
*  Rename folder to pdf.js-[new short hash] with `git mv`
*  Update reference to short hash in renderer.php

New release checklist
---------------------
*  Validate styles.css via <http://jigsaw.w3.org/css-validator/>
*  php -l on all php files individually.
*  Run the Code checker Moodle plugin on mod/pdfjsfolder, excluding
   mod/pdfjsfolder/pdf.js-rybena (adjust line breaks to pass code
   checker).
*  Push to Github.
*  Draft a new release on github (e.g. "v1.00").
*  Download code (zip).
*  Go to https://moodle.org/plugins/view.php?plugin=mod_pdfjsfolder,
   click on the "Add a new version" link in the administration block
   bottom right.
   *  Add zip file.
   *  Check "Rename root directory".
   *  Check "Auto remove system files".
   *  Check "Rename README".
   *  Select Moodle 2.5 in the select box.
   *  Click "Continue".
   *  Add change log to release notes (could be several versions).
   *  Add "Change log URL" (click on the CHANGELOG in Github to get url).
   *  Add "Alternative download URL" (get the URL from the releases page on Github).
