Add node iteration API for the C code
Closes #230 (closed).
- Implemented
DoubleEndedIterator
for thenode.children()
iterator; - Added C functions for using the
node.children()
iterator; - Added tests for the iterator and for the C functions;
- Replaced all uses of
rsvg_node_foreach_child()
with the iterator functions; - Got rid of
rsvg_node_foreach_child()
andNode::foreach_child()
.