Fix memory leak

[jrobichaud]

This code from

python/pdal/PyPipeline.cpp

Line 169 in 3d94698

Array *array = new python::Array;

    for (auto i: pvset)
    {
        //ABELL - Leak?
        Array *array = new python::Array;
        array->update(i);
        output.push_back(array);
    }

allocates an array for each pvset but the arrays were were never released. This PR Fixes this by releasing the memory of the c++ arrays used to pass the data to the python binding.

Closes #23