Attempt to make our markup respect the docbook specification(!), major changes

Attempt to make our markup respect the docbook specification(!), major changes
required:
1) added <para> wrappers where missing
2) added titles to tables
3) removed empty <thead> elements
Point (3) make yelp now shows rules in tables used for syntax references. IMO
this not a good reason to have empty <thead> elements, since they violates the
docbook DTDs. Either yelp should be fixed to not ignore frame/rowsep/colsep
attributes (as it currently does) or we need to find a different markup for
displaying EBNF like grammars.