Cleaned up Python bindings to restore functionality:
* StaticPersistence is iterable, its nodes are usable (sign, pair, cycle)
* StaticPersistence knows how to map its nodes into Filtration indices
* moved PythonCmp into utils.h
* minor cosmetic changes
#include <boost/python.hpp>
#include <boost/python/iterator.hpp>
namespace bp = boost::python;
#include "chain.h"
void export_chain()
{
bp::class_<VChain>("Chain")
.def("__iter__", bp::iterator<VChain>())
.def("__len__", &VChain::size)
;
}