This commit brings in an HLint configuration file
and several recommended modifications such as:
* End-of-line extra spaces removal;
* Import lines ordering;
* Redundant $ removal;
* Generalisation of ++ and map to <> and fmap;
* Preferring `pure` over `return`;
* Removing extraenous extensions.
And finally, a `stylish-haskell` helper script
that detects if code files are dirty. Can be useful for CI,
although manually calling it can be nice if you would rather
first implement then beautify.
