Typedoc - initial config

[kum-deepak]

This attempt seems to have better than my previous attempts:

• Used library mode of typedoc, which is a work in progress, but suits us - Support for library mode TypeStrong/typedoc#1184 (installed typedoc@next).
• All items that need not be exposed in documentation would be marked @internal.
• In the future we will add the following to tslint rules:
  - https://palantir.github.io/tslint/rules/completed-docs/ to enforce documentation completeness
  - https://palantir.github.io/tslint/rules/no-redundant-jsdoc/ to cleanup jsdoc tags which are no longer needed