std::string support is broken

[mmarczell-graphisoft]

This code

class SomeClass {
    public:
    std::string SomeString () {
        return "Hello";
    }
};

#include "nbind/nbind.h"

NBIND_CLASS(SomeClass) {
    method(SomeString);
}

and then invoking the method from JS fails at runtime with

Uncaught TypeError: Module.Pointer_stringify is not a function

Pointer_stringify was removed from the emscripten SDK and replaced with UTF8ToString.