[fpc-pascal] OS/2 INF help support

[Marco van de Voort]

In our previous episode, Tomas Hajny said:
> >> aware of a CHM viewer for OS/2, which is an important downside for me
> >> personally, of course ;-) ).
> >
> > Then fix the textmode IDE for OS/2 :-)
> 
> Would it start working as a general CHM viewer then (including e.g.
> display of embedded pictures in text mode)? ;-)

No. Lazarus lview then.

> > Point is the CHM support is quite far atm, and I don't think it makes
> > sense
> > to add another format. I'm also seriously thinking to cull some of the
> > legacy formats out of the IDE when the transition is ready.
> 
> Fine, let's discuss this (dropping of formats) on case by case basis. E.g.
> OS/2 API documentation is only available in .INF. Dropping .INF
> automatically means dropping support for these documents.

Not dropping the umpteen formats makes any progress on the helpfile front
hard. The "portable" architecture based on integers doesn't fit well with
formats that base on strings as topic-key. Also disambiguation of keywords
in multi-file aggregates would have specific treatment and tradeoffs for all
formats.

And since the supported formats already have readers, people still
interested in them can make a converter app. Same result, same format
support, but at the expensive of minimal work (converting legacy formats),
the IDE-help can be easier optimized.

Note that this is still a vague notion. It was a bit pain to implement CHM
sometimes (html cuts some corners, specially on inter-file links), but
currently it works. It will depend on how the features just over the horizon
will require changes to the helpsystem. 

Most of that stuff is related to combining central indexes, full search, the
caching of those and collecting enough context (_fast) to be able to show a
proper disambiguation dialog when F1 is pressed on a keyword that has
multiple entries.