DeprecationWarning: invalid escape sequence '\S'

[rnestler]

I get a DeprecationWarning from filterpy/common/helpers.py:364

filterpy/common/helpers.py:364: DeprecationWarning: invalid escape sequence '\S'

It results from the invalid escape sequence in a docstring:

    """
    Computes the sum of the outer products of the rows in A and B

        P = \Sum {A[i] B[i].T} for i in 0..N
        ...
    """

I guess this is already fixed on master, since there it's using a raw docustring (r""")? But an easier fix would probably be to use "\Sum".