rename mkfilelist to mkstatus
add github repo info to diagnostics in ``luaotfload-tool.lua``

this is still **experimental**. what to expect:

* the JSON parser in ``util-jsn`` needs fixing. currently it will
  fail if an API response contains escaped double quotes.
  see: <http://www.ntg.nl/pipermail/ntg-context/2013/074052.html>;

* requires the ``luasec`` module for https requests;

* may break in unexpected ways with connectivity problems, e.g.
  timeouts;

* errors not (yet) cumulative with the other diagnostics;

* not yet skippable with ``--diagnose``;

* for the time being API requests are unauthorized. acquiring a security
  token is a TODO.