Revised the cython lab, pages 1,3, & 4. Mainly fixing typos, and smoothing out the presentation.
First version of single pixel lab
Moving forward
Changed travis build so that a failed assertion of the existence of a
Volume's pdf file results in a test failure.
Add assertion of existence of pdf for extra labs to Travis build.
Merge pull request #676 from insertinterestingnamehere/travis

Travis
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
Finished up the lab
Merge pull request #679 from AZaitzeff/SPC

Single Pixel Camera