Make the collapsed navbar smaller

Fixes https://github.com/ocaml/ocaml.org/issues/312
99 problems: better specify the behavior of `insert_at`

Fixes https://github.com/ocaml/ocaml.org/issues/145
Tutorials: Indicate how to use `Graphics` in the toplevel

Fixes https://github.com/ocaml/ocaml.org/issues/130
Remove items collected in `_to-remove`

Fixes https://github.com/ocaml/ocaml.org/issues/290
Add the "Planet subscription HOWTO" to ocaml.org

Fixes https://github.com/ocaml/ocaml.org/issues/232
99 problems: alternative solution for "Run-length encoding"

Fixes https://github.com/ocaml/ocaml.org/issues/129
Replace -- with —
Implement breadcrumb navigation

Fix https://github.com/ocaml/ocaml.org/issues/258
Add CSS rule for Hevea generated blog
Make "Code examples" a link on the "Learn" page

This is to ensure uniformity with the other titles.
Fix redirects of the front page

Check with
http://validator.w3.org/checklink?uri=ocaml.org&hide_type=all&depth=&check=Check
Fix some minor redirects.
Fix all links related to "manual-ocaml"

See https://github.com/ocaml/ocaml.org/issues/90
Fix links relatex to "caml-list".
Fix objcache.ml link

The file is empty so far — it is no longer available on the web.
Fix link to "How to Prove It".
Change the diode graph

The comparison with the diode may be obscure for some readers and is
not completely accurate but leaving it for now.
Removed link to discussions about "OCaml and the web"
Merge the 2008, 2009 and 2011 meetings in the repo

Also remove references to cocan.org (except for "Organization details"
which do not matter much).
Remove dead references to Doug Bagley site