fix Cython version import
fix include of definitions.pxd
remove version spec in travis config
Merge pull request #53 from esc/cython_0.21

Compatability with Cython 0.21
fix typo
Numpy sum will overflow if N too large
Merge pull request #54 from esc/fix_failing_tests_32bit

Fix failing tests on 32 bit
fix typos in RELEASING.rst
fix typo in ANNOUNCE.rst
fix typo