Merge pull request #7 from tshauck/set-difference

Add set difference exercise
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.
Merge pull request #37 from wltrimbl/hopperpicture

replaced richie.txt ascii art with ascii art of Dr. Grace Hopper
Merge pull request #33 from jessitron/gh-pages

Make the opening a little less scary
Growing a program (using a simpler example than invasion percolation)
Adding to the index
Merge branch 'gh-pages' of github.com:swcarpentry/bc into gh-pages
Starting NumPy lecture
Filling in short introduction to NumPy
initial func and modules copy from bootcamps
Anthony's updates to functions and modules.
added Aron's edits.