Add ormolu, remove hlint.

[VictorCMiraldo]

This PR brings in a lot of changes that were produced by ormolu; the important changes are w.r.t. hooking up ormolu to our CI:

• https://github.com/tweag/pirouette/pull/119/files#diff-bc668a2c9f2299cef15b222055b4b4d5311646caec2e7610e540cee18ae9b948L68
• https://github.com/tweag/pirouette/pull/119/files#diff-4df71b389eaed17aa1d651bc8d40d4f67356af9eb04af052c7c5483c0c9f56d1

Closes #105

I advise people to set up a commit hook to run ormolu for you; you can do so by creating an executable file named .git/hooks/pre-commit with the following contents:

#!/usr/bin/env bash
set -e

# command adapted from https://github.com/JLLeitschuh/ktlint-gradle  task addKtlintFormatGitPreCommitHook
filesToFormat="$(git --no-pager diff --name-status --no-color --cached | \
  awk '($1 == "M" || $1 == "A") && $2 ~ /\.hs/ { print $2} $1 ~ /R/ && $3 ~ /\.hs/ { print $3 } ')"

echo "files to format $filesToFormat"
for sourceFilePath in $filesToFormat
do
  ormolu --mode inplace "$(pwd)/$sourceFilePath"
  git add $sourceFilePath
done;

I'll add that to the readme and to the repo on a separate PR used to update the readmes.

[VictorCMiraldo]

I'll merge this unreviewed since it's just cosmetic changes on the code; I'll use some of my time to solve the merge conflicts that this will cause.