Implement pyfaut.Faust.__matmul__() (@ overload), dot() and change __mul__()...

Implement pyfaut.Faust.__matmul__() (@ overload), dot() and change __mul__() to rely on @ when it applies.

Replacing in Jupyter notebook 'Faust_manipulation' the * by a @ or dot() to use same operator as numpy.ndarray but it's the same as * (when used on a Faust object, but it's not supported in python2).
Other unrelated minor changes (typo etc.).