revise euclidean algorithm

Euclidean algorithm only works with integers.

Also added package to Vol1.tex so that it compiles without errors.
added some content

Added a popular editor for Mac OSX.  Also added a little blurb about
ipython.
Merge pull request #76 from ayr0/python_tut

Fixes to Getting Started
fix counter for problems

Make counter for problems behave more nicely.  Also move all commands to
command.tex
Merge pull request #77 from ayr0/counter

fix counter for problems