Remove polymorphic variants in the 99 problems.

While polymorphic variants are elegant, they are an extra concept to
understand and are therefore not desirable in a tutorial.
Highlight strings in OCaml code.
Also highlight empty strings.
Launch a separate toplevel for each HTML file.

The toplevel is executed in a separate process which can be started
and stopped at will (for each HTML file that executes a toplevel
sentence ATM).  The advantages are that the camlp4 extensions loaded
for a page do not influence the other pages and that the main "build"
program can be compiled to native code.
Better indent function definition.
Properly highlight ;; in programs.
Force the linking of some modules in Code_top for Camlp4.
Rename Main into Ocamlorg to avoid a clash with compiler-libs.
Improve the "foreach" tutorial.

In particular, make pa_foreach3 compile and use it in the toploop.
Require weberizer (>= 0.7.6): correct inclusion of .ml files.
added a more modern favicon

I'm not the author of this favicon,
it comes from the link on opam.ocamlpro.com to ocaml.org
http://opam.ocamlpro.com/ext/img/ocaml.png
(I've edited it a little in Gimp though to optimise it a little
for a very small favicon size.)
typo

(PS: the .ico format instead of .png provides compatibility with MS/IE)
mailing_lists.fr.html: iso-latin-1 --> utf-8 (in order to match the actual coding with the one declared in the head)
Merge pull request #171 from pw374/master

mailing_lists.fr.html: iso-latin-1 → utf-8
Merge pull request #170 from blue-prawn/master

Replace the old fashioned favicon from the old website with a more modern one.
Remove OCAMLRUNPARAM=b (no longer needed).
Load str.cma when needed in the Stream tutorial.