Fixes numpy array initialization compile error

Fixes the following tests whihc fail on Yosemite:
test/test_functions.py::test_create_empty_array FAILED
test/test_functions.py::test_create_zeros_array FAILED
test/test_functions.py::test_create_ones_array FAILED
Cast generated C code to npy_intp

According to comments on PR #31.
Merge pull request #31 from iankronquist/yosemite-function-fixes

Fixes numpy array initialization compile error (OS X Yosemite problem)