Merge pull request #86 from wltrimbl/removeis

Removed is from boolean operators (thw-python refinements)
Removed spaces before colons per PEP8
Add @ahmadia suggestions
Merge pull request #58 from r-gaia-cs/teach06-replace

Example find and replace in bash variable
first attempt at a new student lesson
fixed some formatting and grammer errors
proposed replacement for shell-overview
Whitespace PEP8
Merge pull request #84 from wltrimbl/knightsrewrite

Simplified knights example to use straightfoward if instead of for...else.
Added explicit exposition on half-open nature of list indexes
Navigation notes for ipython
Markup prettify
Recited meanings of three fundamental data types.
Removed needless apology
Typos and markup in new sentences
Added line about print syntax
Fixed the copious spelling errors
fixed 'grant_proposal' directory errors
Changed GitHub URLs from SSH to HTTPS

In general, GitHub seems to prefer HTTPS over SSH, and they provide good
support to use it for read-only and read-write repositories on their
site.  In general, HTTPS is more fool-proof than SSH.  In this commit
I've replaced our root-level advice on cloning repositories with HTTPS
URLs.
revert tab completion to 'twice'