[tex4ht] SVG production

[Karl Berry]

    since we have dvisvgm

Ok, good.

    Another question: does it still make sense to use Dvips and GS for PNG
    conversion? Shouldn't we use Dvipng by default? It produces much better
    results.

dvips|gs is probably considerably more widely available than
dvipng in principle, but not among people using our latest tex4ht.

So by all means, go ahead and change things to use dvipng. I'll wait for
that to update TL ... --thanks, karl.