Document public API on main website

[mehulkar]

Add the API reference here: https://cli.emberjs.com/release/api-documentation/

There's probably some infrastructure work to make this happen automatically, but I think we can start by manually documenting the methods available to an addon in index.js? I don't think the methods change very often. Here's the list (taken from https://ember-cli.com/api/classes/Addon.html):

• config
• blueprintsPath
• includedCommands
• importTransforms
• serverMiddleware
• testemMiddleware
• postBuild
• preBuild
• outputReady
• buildError
• included
• shouldIncludeChildAddon
• setupPreprocessorRegistry
• preprocessTree
• postprocessTree
• lintTree
• contentFor
• treeFor

[mehulkar]

These docs also need to do a better job of explaining when to use which hook