Add image_medium_size variable in the templates
Add thead, tfoot in default default_good_tag_list
Test if file is already imported and close ic
Fix: output_hashtbl should now work for OCaml 4.00+
Moved css to an external file to benefit from caching.

Properties using variables still need to be in the .txt file, but this should be improved.
Do not support non-UTF-8 bases any longer

Got rid of the global reference utf_8_db and some dead code.
Update deprecated functions
Array.create -> Array.make
Lazy.lazy_from_fun -> Lazy.from_fun
Preparing for safe_strings
configure: check ocaml version
Compile with opam and OCaml 4.01