Added combined lesson writing code for people
Merge remote-tracking branch 'upstream/2013-08-uwmadison' into 2013-08-uwmadison
Added combined lesson dont repeat yourself
Added ipython intro lesson
Remove ipython content from writing_code_for_people

The ipython content is now covered in the ipython lesson.
Add hello.py to ipython intro directory
Add condition & emphasis on code readability

Conditional section is copied from dont repeat yourself / flow control.
Emphasized code readability considerations for variable name & type
choice, white space and comments.
Remove conditional section
Add whtespace to summary
Add pasting help, docstring emphasis, minor changes
Added Set content back
Fix typos
updated links to other sessions
Merge pull request #28 from jensv/2013-08-uwmadison

shortened python sessions