New features: link formatting, real date filters

Features:
- the displayed link can now be formatted using any of the available
meta columns (incl. normal Dokuwiki metadata fields).  E.g.
dislay={name} ({cdate})
- the filter option now correctly recognises dates and provides a method
for filtering by them. Uses the PHP strtotime function.  E.g.
filter=mdate:2 months ago->
- namespace headers are now links to their namesapce

New options added:
- showcount: show the result hit count
- hidejump: hide the 'jump to top' link
- dformat: the date formatting for the new link display formatting

Removed/changed deprecated features and names:
- changed: nomsg (hidemsg), nostart (hidestart), count (showcount), jump
(hidejump)
- removed: useheading (display...), abstract (snippet), inwords
(spelldate)

Bugs:
- casesort option was not functioning
- fixes to mgroup algorithm