github helper
## Features
##### 1. Duplicate issue button [Complete]
Although this feature is complete, it is fragile.
It will not work if the html design of github is changed.
As of 2019-03-01, it is working.
##### 2. Sort the issues in the project by assignee [Under development]
##### 3. Suppress Commit Links[Complete]
Github has `Autolinked references and URLs`.
However sometimes they are noisy.
So suppress comment links.
##### 4. Add outdated button for comment hiding [Complete]
Github can hide comment.
But it requires a lot of action.
So add `outdated` button for hiding comment.