Rename rectangle module to rect. #4.
To deal with case-insensitivity on Mac.
Add C callback pi calculation example.
Remove attempt at multi-pxd file compilation.
Appears to be a cython limitation.
Support multiple .pyx files, .py files in cython_add_module.
Add pxd files from cimport statements to dependencies.
Add dependency checking for corresponding .pxd file.
Also move the *.h and *.pxd to their own include directory.