Initial attempt at popups - doesn't quite work yet...
Merge branch 'master' into hints

Conflicts:
	stack/cas/castext.class.php

Added a sub of a hints class.
Updated the hint system to use the syntax [[hint:tag]]
Changes to enable older questions to work.  Still need to fix the editing side, so when a question is loaded the old <hint> is converted to a new [[hint:...]
Change the design so that old <hint> tags are quietly supported.  I still need to make sure these are converted when we load a question to edit it.
Update the edit_form to convert old <hint> to the new style [[hint:..]]
Further tests.
Minor update to the docs.
Merge branch 'master' of github.com:maths/moodle-qtype_stack