Missing svg namespace for path elements added to doc tree using document.add_path()

[neel-stark]

https://github.com/mathandy/svgpathtools/blob/3a1fe8695dd6236af81b5477714e74a094e3b088/svgpathtools/document.py#L327

Inskscape is not able to recognize the paths added using add_path(), due to the missing svg namespace.

the following modification, (similar to what has been implemented for adding groups in line 415 of the same file (document.py)) solves the issue:

return SubElement(group, '{{{0}}}path'.format(SVG_NAMESPACE['svg']), attribs)