Update docs on V3

[mhoeger]

Update documentation on V3 functions host + javascript:

• introduce way to revert "[breaking]"
• [breaking] throws on Node.js v8, keeps 8 binaries for V2 host compatability
• fully support node.js 12
• [breaking] does not duplicate http payload in context.bindingData
• [breaking] fixes HTTP output through context.done(null, res) and $return is not handled correctly #228 (handles http output correctly on context.(null, { body: "hello" });
• [breaking] fix camelCase of timer trigger object: camelCase Timer Trigger object #188
• [breaking] fix type conversion of code like return { outputBinding: info, outputBinding2: info };: Node: Blob output binding should support passing a Buffer #232
• [breaking] in host and worker, make sure http payload "as raw" as possible
• [breaking] rawBody http property should not be a UTF-8 string for byte data (rawBody http property should not be a UTF-8 string for byte data azure-functions-host#4475)
• [breaking] consume "TypedDataCollection" Event hub, Binary datatype and Cardinality many #262

[mhoeger]

Jeff has this covered