Migrating to Python3

- Modify PubChemPy to support Python3 (no backward compatibility with
Python2).
- Unit testing passed successfully.
- Add IPython notebook based on unit testing.
Merge remote-tracking branch 'ekaakurniawan/master' into python3
Merge branch 'master' of github.com:mcs07/PubChemPy into python3
Fix urllib imports to work with both python 2 and 3
Fix string type checking to work in both python 2 and 3
Remove python 3.4 from travis-ci, not available yet
Fix string encoding/decoding to work in both python 2 and 3
Add python version information to docs
Tidy up python3 stuff
Remove ipython notebook for now
Merge pull request #4 from mcs07/python3

Add backwards-compatible Python 3 support