Added a solution for laying out binary trees(2)

This one spaces the nodes based on how far they are from the bottom of the tree, 2**(h-d-1)
Added height, adjusted indentation
Merge solution for laying out binary trees by joelwilliamson
Minor reformatting of the 99problems "Layout a binary tree 2" solution
Add a conclusion to "Data Types and Matching"

Explain slightly more what the exhaustiveness of pattern matching
means.  Fixes the first request of
https://github.com/ocaml/ocaml.org/pull/165/files#diff-7aa1248a16bc967c3c0d4a7a7caab077R271
Minor corrections

Inspired by
https://github.com/ocaml/ocaml.org/pull/165/files#diff-7aa1248a16bc967c3c0d4a7a7caab077R271
Update all links to the OPAM universe index with new opam-compatible URI
Merge pull request #506 from dsheets/pkg-redirect

Update all links to the OPAM universe index with new opam-compatible URI
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