Add external dependency to jq
Add external dependency to jq

The tests depends on conf-jq, a virtual package that ensures that jq
is installed.

Since jq is required _before_ the installation of opam dependencies, reorganize
the steps to require the installation of external dependencies (jq and
tidy-html) before the development setup.

1. Install requirements
2. Set up for development
...

ocaml-doc/odoc,ocaml-doc/odoc