DOC: update .pyx docstring
Add timestamp checks to checklist.py for Cython code

Compares the timestamps of generated C files and Cython files to ensure that Cython files are not newer than the generated C file.
DOC: add changelog mention
Update generated C code

Thanks checklist.py :P
Merge pull request #609 from jairideout/checklist-cython-timestamps

Add Cython/C file timestamp checking to checklist.py