coverted tutorial to ipynb
reconstituted markdown version of shell tutorial
updated variables.ipynb
Converted tutorial to ipynb
updated data structures notebook
updated flow control notebook
Merge scopatz 'flow-cont' PR 21
Merge scopatz 'vars-types' PR 18
Merge scopatz 'data-struct' PR 20
Merge scopatz 'strings-io' PR 19
added explanation about comparisons, genotype example details
renamed variables, avoiding camelcase
added inline exercise with tests, light-handed change of variable names
Removed math.log example and replaced half-baked examples with more concrete elementary ones.
Expanded examples and converted notebook to v3.
Converted debug tutorial to ipython notebook.
updated debugging tutorial.
Replace Python with Shell

In the box "Text vs. Whatever" it say Python when should say
Shell.

I move this box two paragraphs up to be closer of the lesson
part about writing the file 'middle.sh'.
Replace "Shell" by "shell"

As point out by @ahmadia we don't use "shell" capitalized (see the
Wikipedia entry: http://en.wikipedia.org/wiki/Shell_(computing)).
Cite shell parameter expansion

This is part of Issue #54.

In this commit we mention the shell parameter expansion to make
easy to students go deep if they need.

We also add a note about use ${some-var} instead of $some-var.