Replace ModuleThis type with YahooFinance type, handle schema generation functions, common code

[gadicc]

• Still from v2, modules use this: ModuleThis, we should mvoe to YahooFinance type.
• ts-json-schema-generator can now handle functions and represent them with comments and props in JSON. We need code to handle that.
• The common types are repetitive, we should export them once somewhere and modify schema-gen.ts to import and remove dupes.