Added functionality:
* Begin_Macro/End_Macro, Begin_Latex/End_Latex (generate images, see
TDocParser's doc for now)
* module documentation (e.g. html/doc/index.html)
* help on help (savannah bug #20755)

Separate parser and output generator; public interface stays in THtml.
Create a "hook" for directives like Begin_Html/End_Html etc, to make it
easily expandable.
New layout, bug fix (savannah #20472).
Missing: lots of doc. Rule checker fixes  :-)


git-svn-id: http://root.cern.ch/svn/root/trunk@17762 27541ba8-7e3a-0410-8455-c3a389f83636