Hi,

This patch adds some general interest(?) symbols to org entities that
otherwise lived in my init file.

1. I don't know how to easily check whether a glyph is supported by
   Latin 1, so Latin 1 entries correspond to the ASCII equivalent.

2. HTML symbols have been tested in Firefox.  In a few cases I
   couldn't find a pretty name (like "π") in which case I've
   supplied the unicode number (like "&960;").  Is that OK?  (E.g. can
   Org produce non-uft8 HTML?)

3. In LaTeX the symbols are mostly defined in amsmath, except coloneqq
   and eqqcolon which requires something like mathtools or kpfonts or
   possibly unicode-math.  Is that OK?  I also fixed some
   inconsistencies.  E.g. loz was loaded diamond even though loz is
   defined in amssymb and "~" and "\tilde" produced different results
   (the latter produces the irritating "\~{}" often observed among
   (social science?) university professors...).

–Rasmus