Use HLint3.hlint in Lint

[lierdakil]

Related: #826

So, this seems to work fine, although passing --quiet seems a bit more brittle than it should be.

@DanielG, up to you if we want to use this or wait until hlint upstream fixes (I will report an issue soon)

[DanielG]

Looks good. Are there any downsides to using this?

[lierdakil]

Well, the main downside is basically substFile. While with other approach we can just pass the filename and file contents, here we have to replace filename in post. Also we lose control of input file encoding, but hlint uses utf-8 by default since 1.9.12 I believe (ndmitchell/hlint#96)

[lierdakil]

Also worth noting that if '--quiet' is omitted (or syntax ever changes for some ungodly reason), hlint will spew its output to stdout, in addition to returning [Idea]. Tests should catch if it goes awry. In any case, hlint function comes with the following warning:

Warning: The flags provided by HLint are relatively stable, but do not have the same
API stability guarantees as the rest of the strongly-typed API. Do not run this function
on a your server with untrusted input.

[DanielG]

sounds reasonable