New: svg represented as pugixml objects instead of strings

-svgdevicecontext include file now contains node stack and current node

-nodeStack, xml declaration node, and main <svg> node are created in constructor of deviceContext. <svg> height and width are set in Commit as scaledHeight/Width are calculated later.

-All WriteLine code was replaced with pugixml equivalents.

Next commit will clean up any old fragments of code still remaining.
Fixed: removing one line

Accidentally left an additional debug statement in.