Method index

test/histogram_test.cpp:663–663

the customization point - accept const char* and convert to int - then call index method of base class

      // - accept const char* and convert to int
      // - then call index method of base class
      int index(value_type s) const { return integer::index(std::atoi(s)); }
    };

    auto h = make(Tag(), custom_axis(0, 3));