Add haddock comments

[snowleopard]

Current implementation of concepts lacks Haddock comments. We need to add them as part of converting concepts into a library package and putting it on Hackage.

Haddock syntax: https://www.haskell.org/haddock/doc/html/ch03s08.html

[mvdan]

When you publish a Go package with inline comments (docs), you can then link to godoc.org like this:

Makes it really easy to navigate the docs, especially via the badge. Is there a service like this for Haskell? I couldn't find anything on a quick google search.

[snowleopard]

I think there is a Hackage badge, e.g.: https://github.com/ndmitchell/shake.

And docs are shown very nicely on Hackage, e.g.: http://hackage.haskell.org/package/shake-0.15.5/docs/Development-Shake.html

[mvdan]

Ah, okay then.