[#5] Implemented GitHub Integration

- Implemented GitHub API calls:
  - Get files form PR.
  - Get all comments from PR.
  - Create review comment for file in PR.
- Improved the data representation for results (file, rule and item) from records to maps. 
- Updated README.
It doesn't seem to [Issue #77[(https://github.com/cmullaparthi/ibrowse/issues/77):

>The application using ibrowse is expected to issue another request with the new URL when it encounters a redirect.