html validation fixes:

html validation fixes:
 - escape & in urls (also clean up cgi url generation)
 - since markdown wraps inlined pages in <p></p>, close and re-open
   the paragraph tags when generating the embedded html
 - added XHTML 1.0 doctypes to templates
 - fixed <hr /> and <br /> in templates
 - add an alt attribute to inline images, based on the WikiLink to the
   image. Allows things like [[my_image|img.png]] to customise alt text.