Improvements to cython-mode.el

I have finally gotten around to updating the cython support in [sage-mode](https://bitbucket.org/gvol/sage-mode/src), and decided it would better if I just used the official cython-mode.el.  But rather than just switch, I would like to port a few improvements that were in sage-mode's version.

The first few commits, are from yours truly, original work etc.  The last 3 were ported from sage-mode written by Nick Alexander and released under the GPL.  I have seen [other versions of cython-mode.el](https://github.com/gorakhargosh/emacs-kit/blob/master/cython-mode.el) (basically identical to the official version) on the net claiming to be GPL, but Cython itself is Apache IIUC.  Therefore, I'm not sure of the legality of including these last patches.  In particular, it would be great if cython-mode.el clearly stated the license it was released under.  I am willing to rewrite them to avoid potential problems if need be.