added save and restoration of lines generated by turtle; reworked save and restoration of bitmap so that old bitmap will be reused only if it's dimensions match exactly with screen dimensions, otherwise new bitmap will be drawn from scratch;
added save and restoration of lines generated by turtle;
reworked save and restoration of bitmap so that old bitmap will be reused only if it's dimensions match exactly with screen dimensions, otherwise new bitmap will be drawn from scratch;

sergv/turtle-geometry