Compat

All files in the `quantecon` package should be python 3 compatible now.  All files except `wb_download.py` should be python 3 compatible in the examples directory.  The file `wb_download.py` wasn't as clear how to go about fixing as the others because of changes in the structure of urllib and urllib2.  I think that is a minor thing that can be taken care of in the near future though.  Submitting PR.

Note: Using this one instead of other PR because I had pulled some of the tests branch and deleted those files which would have caused issues with pulling the tests branch later.  Spencer did some git voodoo (cherry-pick) to fix it.
I had to add these lines to make it compatible with python 2 and python 3.

This obfuscates the example a bit. I think it is probably worth it so that this isn't the only file we have that doesn't run on python 3, but I wanted to get other thoughts.