Various fixes

I decided I would fork a project that was a fork of my project so I could submit fixes to the fork. :stuck_out_tongue: 

* Use proper 2 space indentation
* Convert mixed tabs and spaces to all spaces
* Fixed string concentration errors (`+` signs go on the end of the line)
* Fixed location of new script files in generated HTML (they need to be inside the closing body tag, not outside)
* Restored menu registration (#5 removed all access to extension instead of just the shortcut by mistake)
* Update GitHub download link in Readme
* Update usage directions in Readme 
* Updated package.json for last release (remember to do this before making a release! :wink:)