ocamlorg.css: replace absolute paths with relative paths

This makes the local absolutization of CSS paths a no-op.
Merge pull request #507 from dsheets/relative-css

ocamlorg.css: replace absolute paths with relative paths
Remove the transformation of absolute paths in CSS

This is no longer necessary because of commit 92cf425
Scheme-relativize a couple links in prep for https
Merge pull request #509 from dsheets/relative-scheme

Scheme-relativize a couple links in prep for https
Make scripts before launching the parallel page build

Fixes https://github.com/ocaml/ocaml.org/issues/508
Lighter make output
Depend on opam-lib implicitly through opamfu

The findlib library opam-lib used to be called just opam so we rely on
opamfu to depend on the right one.
Begin a basic merlin project description
Move URL mapping into a new Urlfun module, fix small bugs in relative_urls

In particular, having a host is what makes a URL on relativizable, not a scheme. Also, made the CSS map function operate over all url() values (not yet those with double quotes).
template/: Add some customizations to main.mpp
template/: Allow Contact links in footer to be customized
script: add absolute_urls to generate a site template for subdomains
script: fix a breadcrumb.ml bug that was removing a leading /
script/relative_urls: convert to use almost all Uri functions, Urlfun util module
opam.ocaml.org: generate an opam.ocaml.org template
opam.ocaml.org: Ignore the generated template
opam.ocaml.org: template build update
Improve French installation page

 * Added missing comma
 * Removed reference to OCaml version
 * Translated comments to French
 * Fix Markdown formatting
opam.ocaml.org: add subheader and superfooter

Make title clearer, remove custom contact section, add subheader, superfooter, extra js section