Module loader now loads non-module files also:

- Changed MO5() to load non-module files via AJAX, when
  the module "name" begins with "ajax:" followed by a URL.
  The XMLHttpRequest object used for the request will be
  given to the callback depending on it no matter whether
  the request failed or succeeded. You need to check that
  for yourself!

- Changed MO5.ajax module to be a simple wrapper again and
  added the ajax function to MO5.js file so that it is available
  as MO5.ajax globally. This was necessary because MO5() now
  needs AJAX functionality again and we don't want to
  duplicate any code.
Added MO5 Script standard library, commented out debug logs:

- Added an MO5 Script standard library file written in MO5 Script.
  It will automatically be loaded and linked in to the Interpreter
  before executing any other code. The library right now contains
  only the "when" macro, but is expected to grow in the future.

- Commented out console.log calls used for debugging, but leaving
  them there for the time being because the script infrastructure
  is pretty alpha still.
Added macro progn to the MO5 Script standard lib;
not sure if that's such a good name for the purpose,
though. It will probably change later on...