Add remark

[vweevers]

Best to follow the commits (the last one adds a lot of style noise).

[vweevers]

Q: should we remove contributors from package.json now that we have CONTRIBUTORS.md?

[vweevers]

And the code comments as well? E.g.

levelup/lib/levelup.js

Lines 1 to 5 in a6e852b

	/* Copyright (c) 2012-2018 LevelUP contributors
	* See list at <https://github.com/level/levelup#contributing>
	* MIT License
	* <https://github.com/level/levelup/blob/master/LICENSE.md>
	*/

[vweevers]

I accidentally relied on a npm-linked remark-git-contributors, need to release a new version first to ignore greenkeeper commits.