Missing docs for SQL functions

If I'm not missing something completely obvious, the core tutorial at https://www.stackage.org/haddock/lts-10.10/esqueleto-2.5.3/Database-Esqueleto.html doesn't really teach how to use SQL functions/expressions, such as date, random, now, substr, etc.

Coupled with the fact that the modules Database.Esqueleto.SQLite and Database.Esqueleto.MySQL don't show up in the package contents, I was under the impression that Esqueleto had absolutely no way to groupBy date(timestampCol) in SQLIte. After going through https://github.com/bitemyapp/esqueleto/blob/master/src/Database/Esqueleto/PostgreSQL.hs I realise that unsafeSQLFuntion is that escape hatch.

• Are you open to a PR that documents this in the main tutorial?
• Are you open to PRs for adding more functions to https://github.com/bitemyapp/esqueleto/blob/master/src/Database/Esqueleto/SQLite.hs