[GRASS5] 5.1: --html-description to parser added

[Markus Neteler]

Derived from the --interface-description there is now
--html-description
available in the 5.1 parser (CVS).
 
e.g.
d.erase --html-description > d.erase.html

will generate a valid HTML file containing parameter(s) and flag(s)
description in the well known style of the GRASS man pages.

It may be discussed if we add something like
option->longdescription = "long explanations";

to the modules to move extra explanations from the HTML files to
the module itself (now sometimes the parameter/flag descriptions
are identical to what the module's help text provides, sometimes
the descriptions differ which is no good solution).

Markus