MVP
===
- lint everything
- delete lint on close file

TODO
====
- lint current file
- [v] command clear all issues

Long Term Desired Features
==========================
- Fancy UIs for
    - arc patch
    - arc todo
    - arc unit
    - arc browse
    - arc paste (upload and download)
- list open Differential in repo (for review)
- get hovercard (content) for any object
- push notifications from website ?
- preview Remarkup
- some magic to help the External Editor Link
- arc lint: special-case some messages for better visibility (find more range/information.)
- arc lint: support auto-fix (apply diff)
- arc lint: `locations` field may be parsed into `relatedInformation`.