Added pathFromSVGString and pathFromDAttribute factory methods

These are useful for those who have complex SVG-files or embedded SVG that they want to parse themselves and leave just the path conversion to PocketSVG. (In my case I'm parsing KanjiVG).

Considering how small a change this was the need for this must have been completely nonexistent or I have failed to see some design decision that this was undesirable?