Tweaks to Dia for chemical diagrams

[Dave Linton <djl27 hermes cam ac uk>]

I'd like to be able to draw molecules in Dia, mostly because the de facto
standard, Cambridge(no relation)Soft's ChemDraw, is absolutely awful.
As far as I can see it would only require a couple of extensions:

- a triangular grid option (most important!)
- text with bounding box (for my purposes filled in background colour, so
  that letters on top of lines are easily readable
- line styles which taper from one end to the other
- ditto, dotted (i.e. made up of small lines perpendicular to the line
  direction)

I can't check right now that none of these are already in there, so try
not to abuse me if they are :)

rgds
David Linton
.