Mapping yml to FAQ json and vice versa

[hailiang-wang]

Description

parent https://github.com/kaiyuanshe/osschat/issues/153

Define a yml schema, consider the properties that can be mapped into a FAQ JSON file.

• Question (required)
• Answers (multi plain text only now, required at least one item)
• Categories (with a single key and value, optional)
• DocId (optional , can be generated automatically, possible solution, auto generate with Quetion hash, reserved key)
• Extend Questions (optional)

[hailiang-wang]

考虑在 https://github.com/chatopera/chatopera-nodejs-sdk 中增加新的类，比如 Utils 来实现接口。

[huan]

Link to #179