[fpc-pascal] FPImage and GetDataLineStart

[Marco van de Voort]

In our previous episode, Michael Van Canneyt said:
> > If you declare your class as e.g. TBW32image (RGBA), a pixel assignment is
> > an inline handful of instructions.
> >
> > I think fcl-image with its no-compromise format support was great initial
> > effort.  But it is time to at least allow some internal shortcuts for
> > performance's sake. And generics allow a way to put this into a class
> > hierarchy without too much code duplication.
> 
> You can propose whatever you want _but_ generics.

Motivation?