Removing explicit 'level' keys from Markdown files
*   Getting rid of old cheat sheets
*   Indenting error output cells
*   Removing explicit 'level' keys from Markdown files
*   Storing the generated files so that people who don't use those tools won't have to regenerate them.
*   Modifying .gitignore to reflect this.
*   Updating the Makefile to run Jekyll exactly once.
*   Command to install on the server
*   No longer worrying about making a page of images
*   Better (more guessable) name for the target that builds the website
*   Fixing image paths
*   Fixing up glossary entries
Merge branch 'sticking-with-jekyll' of github.com:gvwilson/bc into sticking-with-jekyll
Drafting a lesson on working with climate data as a wrap-up for novices
Modified build to generate Markdown files for IPython Notebooks in the source directories so that the Jekyll build will put all the files in the right places.  (Having a separate CACHED directory is cleaner, but then we have to move or patch files after the fact to make links resolve.)
Starting to convert to notebook
Converting a bit more to notebook form
Markdown version of climate example
Converting climate data example to notebook form
Merge branch 'master' into worked-example
Polishing the data download example
1.  Merging fixes for missing image files from @r-gaia-cs.
2.  Putting IPython Notebook stuff in a separate Makefile so it won't inadvertently trigger when doing a regular site build.
    This ensures that people who *don't* have IPython installed,
    and don't want to re-create the Markdown files for notebooks,
    won't accidentally try to do it.
Fixing bug in code example
Markdown version of spatial intro
Adding image files produced from IPython Notebooks
Moving Python climate data example into 'extras' directory
Avoiding confusing terminology
Merge pull request #428 from gvwilson/splitting-makefile

Simplifying Makefile and adding documentation.
Merge pull request #431 from mkcor/improvements

Avoiding confusing terminology
Fix name of function in exercise

Noticed in #458. The function name was changed from `normalize` to `center`, but the exercise still referred to `normalize`.