Resolves #59, upgrade to Asciidoctor 1.5.0
Resolves #43, adds a note to README about TOC
Move extension into app directory (and options page into html directory)
Allow the user to load the JavaScript after/before the document has been rendered
Add an example to show how to use custom JavaScript
Switch the default highlights.js theme to github
Prepare 1.5.0.100 release
Update changelog with 1.5.0.100 release
Only source highlight if source-highlighter is hightlightjs

Ref #64