Document final API in docs site

[AaronLeoCooper]

Document API in docs site under API reference once API is finalised for v1.0.0. Notable things to include:

• Complete & tested guide for installation (NPM & CDN) & getting started
• API spec of HTMLApp options
  • appName
  • eventHandlers
  • onLoadApp
  • onUnloadApp
• API spec of HTMLApp public methods
• API spec of element helper methods/properties
• Development tips
• About page
  • About the library & author
  • Contributing details