IHP v1.2 Release

[Marc Scholten]

Release Checklist:

• Pick a release commit (a2b5658)
• Merge into the v1.2 branch
• Upgrade active digitally induced projects over to 1.2 to make sure that everything is stable
• Increment version numbers in ihp.cabal, Paths_ihp.hs and ihp.nix
• Tag the release
• Update the boilerplate
• Announce the new release on newsletter, twitter, reddit, haskell discourse

[Marc Scholten]

#1809 might need to be fixed for this release