Added rips-zigzag; in the process caught a number of bugs in ZigzagPersistence (added check_consistency() to it)
#ifndef __NUMBER_TRAITS_H__
#define __NUMBER_TRAITS_H__
template<class NumberType_>
class number_traits
{
public:
typedef NumberType_ NumberType;
static NumberType& normalize(NumberType& n) { return n; }
};
#endif