added member function to Real python bindings to enable numpy usage

[rath3t]

This enables the usages:

from autodiff import *
import numpy as np


def f(x_):
    y_ = np.array([7.0, 7.0])
    return np.sin(np.power(x_,3)) * y_


x = real(2)
x[1] = 1
y = 2
print("Double sol")
print(f(y))

z = f(x)
print("autodiff sol")
print(z)

which prints

Double sol
[6.92550773 6.92550773]
autodiff sol
[autodiff.real(6.92551, -12.222) autodiff.real(6.92551, -12.222)]

Before this lead to an error message similar to

TypeError: Unable to convert function return value to a Python type! The signature was (arg0: autodiff.autodiff4py.dual1st) -> autodiff::detail::UnaryExpr<autodiff::detail::CosOp, autodiff::detail::Dual<double, double> const&>