Improve French version of mailing_lists.md
The first page in French
Add alt tags on images
Improve index.fr.md baseline
Add a script to translate navbar.mpp
Merge Lefessan's contributions to the French Mailing List page
Add translation "buttons" to the front (core) page
Improve translation script

* Remove "open Printf", which decreases the readability of code
* Remove useless function "language_of_ISO639"
Merge branch 'master' into index.fr.md
Fix to use standard translation links
Fix Tutorials.Modules (fr) header overlaying breadcrumbs and lang selector

Apparently ---- underlining in markdown creates an H2 header which has different styling in bootstrap_mod.css than an H1 header such that the header box ends up catching most clicks on the breadcrumb or language selector links.
Fix Tutorials.Structure (ja) header overlaying breadcrumbs and lang selector

Same as #415
Fix Tutorials.Set (ja) header overlaying breadcrumbs and lang selector

Same as #415
Fix Tutorials.Map (ja) header overlaying breadcrumbs and lang selector
Fix Tutorials.Streams (en) header overlaying breadcrumbs and lang selector
Small improvements to the French front page
Merge remote-tracking branch 'ocaml/master' into translate-navbar
Use a translation file

Translations will be stored in translations/en_to_??.txt with the
syntax:
"english" -> "french" (* or other language, with OCaml comments *)
Translate Array of New Packages
Translate "Search" to French