Added explicit exposition on half-open nature of list indexes
Added link to documentation on lists
Remove git lesson mistakenly attributed to The Hacker Within.
Add Matt's original git and GitHub lesson notes.
Add header material and author to git and GitHub lesson.
git -> Git where appropriate
Merge pull request #133 from jiffyclub/fix-git-and-github-lesson

Fix git and github lesson
Merge remote-tracking branch 'wltrimbl/half-open' into gh-pages

Actually, I merged origin/pr/95, because:

  git://github.com/wltrimbl/bc.git half-open

doesn't seem to exist anymore ;).

Minor quibbles to be resolved later:

* '--' vs. a Unicode em-dash (U+2014 EM DASH), but I'm not sure how
  IPython handles charsets/encodings.
* Bold vs. italics in "elements returned **include** the **starting**
  index but **exclude** the **final** index", because I like:

    * Bold to pick out key terms (page-level emphasis)
    * Italics to stress phrases (sentence-level emphasis)

Neither of those are important enough to keep this out of the main
branch.

* wltrimbl/half-open:
  Added link to documentation on lists
  Added explicit exposition on half-open nature of list indexes
Merge pull request #136 from gvwilson/maint-update

Maintenance update
Merge branch 'master' into new-sql-beginner-lessons