Changed file extension

Changed file extension on mmh-test-answers to .md
Merge remote-tracking branch 'upstream/gh-pages' into gh-pages
Author corrections

Author corrections to first pages, updated images
Merge pull request #15 from emmaattwell/gh-pages

I'm merging this now. I haven't checked all the docs, but we'll have a chance to see if all's well when we output proofs and check web output.