Modified composebox_typeahead.js to recognize the triple backtick
and tilde for code blocks, and added appropriate typeahead functions
in that file and in typeahead_helper.js.
Additionally, a new file pygments_data.js contains a dictionary of
the supported languages, mapping to relative popularity
rankings. These rankings determine the order of sort of the
languages in the typeahead.
This JavaScript file is actually in static/generated/pygments_data.js, as it
is generated by a Python script, tools/build_pymgents_data.py. This is
so that if Pygments adds support for new languages, the JavaScript file
will be updated appropriately. This python script uses a set of popularity
rankings defined in lang.json.
Corresponding unit tests were also added.
Fixes#4111.
Cory Lynch