Revised the cython lab, pages 1,3, & 4. Mainly fixing typos, and smoothing out the presentation.
Further revisions to the language in the second half of the Cython lab.
Merge branch 'develop' into cython_revisions

Merge branch 'develop' into cython_revisions
Merge pull request #678 from joshualy/cython_revisions

Cython revisions