Created post for list and string python exercises

Included code and output for all required exercises, as well as a few comments
Changed output heading formatting
Added additional comments and reflection
Added additional comments to exercises 11 and 12
Added additional comments/reflection

also changed var name in last exercise (s to initial_string) to be more descriptive
Merge pull request #191 from britth/gh-pages

Brittany's List and String Python Exercises