feat: reql format command

[gabor-boros]

Description

Add the new format command.

Code examples

r.table("movies").map({
  id: r.row('id'),
  ratings: r.http(r.format('http://example.com/movies/?title={title}&release={year}', r.row))
})

Checklist

• I have read and agreed to the RethinkDB Contributor License Agreement

References

• feat: add format ReQL command rethinkdb#7066