hexadecimal color names added

The CVS version now has hexadecimal color names, e.g.

set color ACD4EF
set font size 33
draw label "Robin-egg blue" at 3 3 cm

This feature will enter into the stable stream on the next release.

OK, I know it's against the rules to put new features into the stable stream, but what the heck, I want this sort of thing quite often in my own work, since I often decide upon colors by using the gnome terminal color tool, and it doesn't give color components in the 0 to 1 range that gri wants.