[Pyrex] cimport: include path and standard headers

[Eric Huss]

> I wrote these, and I think they cover the entire Python C/API.  It
> would make a lot of sense to distribute them.  They are in this
> directory, if you want to look at them:
>
> http://www.sagemath.org/hg/sage-main/file/b663cbb712d1/sage/ext/
>
> William

I like how thorough you were with adding docs and everything!  I have a
similar file with almost all of the API.  I noticed that a lot of your
definitions are missing the except definitions (except -1 type stuff) so
that Pyrex can generate the correct error handling code.  I can post my
copy if you'd like to compare.

-Eric