Init. commit of (medical) image processing ipynb.
Add height to Eventbrite iframe

and values for when using two rooms.

**The height provided isn't suitable for small screens.**

Close #493.
Made changes suggested by Will Trimble - change Lena for Sally Ride.
Downsampled image to sensible size and removed references to SciPy Lena.
Simplified introduction by removing complicated colourbar placement stages.
Finished cleaning up IPYNB to show Gaussian fit to background.
Move SSH Key lesson from Git to Extras

Close #691.

After some discussion about have and where to put the lesson that
cover SSH Key I and @wking agree to move it to
`novice/extras/06-sshkeys.md` and just add a note + links to help
students set up their own SSH Key for the Git host they will be using.

This commit includes @jdblischak and @wking wording about HTTPS vs. SSH.
Create reference guide for Mercurial.
Update novice r lesson 01 to drop seq
Merge pull request #707 from r-gaia-cs/remove-ssh-from-git

Move SSH Key lesson from Git to Extras
Fix mailto links

Close #748.
Merge pull request #756 from r-gaia-cs/fix-mail-link

Fix mailto links
Fix small typo in novice Python cmdline lesson

Close #747.
Merge pull request #757 from r-gaia-cs/fix-typo-python

Fix small typo in novice Python cmdline lesson
Merge pull request #753 from jhollist/nov-r-1-drop-seq

Update novice r lesson 01 to drop seq
Add note about proxy ...

and symptoms of problem with the proxy.
Incorporate changes from review by @r-gaia-cs.
Delete errant leading / in path.
Merge pull request #714 from douglatornell/hg-ref-guide

Create reference guide for Mercurial.
Merge pull request #489 from r-gaia-cs/proxy

Add note about proxy