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
Use "OCaml Planet" as the aggregated feed title
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.
Merge branch 'master' into syndic
Use the broken feed representation on Http_client.Http_error
Move the functions dealing with HTML in the "Utils" section