[O] format of the ID property in the new HTML exporter

[Daniel Clemente]

Hi,
  in ox-html.el there's a line with an assert (the only one):

           (assert (org-uuidgen-p path))


1.  I have some IDs like "o5y98600aze0" which don't conform to that uuidgen 
format; they were created by early versions of org. Should only UUIDs be 
accepted as ID?
2.  I think the ID should be editable by hand to what you like, as long as they 
are unique. If you don't need to export it you don't need a CUSTOM_ID, and 
having both ID and CUSTOM_ID is not the simplest way.

  So I think that assert is too strict. My short IDs seem as good as the long 
UUIDs.