winhelp: add preliminary *.cnt file support (parser)

[Eric Pouech]

> Also, I stumbled upon the following problem: HLPFILE_FreeCnt is never called! 
> There is something bad with hlpfile->wRefCount - it's 4 (!) instead of 1 
> after just opening and closing file.
>
>   
actually we should decrement the count for:
- closing the window attached to a page
- upon exit, remove references in history (and attached refcounts)
that should help here (not sure I got them all though)
A+