Deprecate python2

[santoshphilip]

List the steps needed for having only python3 version of eppy:

For python2 eppy

• have a clear link were the python2 version of eppy can be downloaded or installed

for python3 eppy (non-code changes):

• do a major version number change
• change README
• update tutorial
• update all other user documentation

code changes for eppy3:

• gradually remove six
• change setup.py file
• there are some python3 deprecation warnings
  • update code for this

@jamiebull1 , If you can think of other items, can you add to this list ?

[santoshphilip]

Make version 6.0.0 release as python3 only

• update setup.py
• Note the following in the README.rst
  • This is a python3 only release
  • python2 is not supported from this release onwards
  • give link to the last python2 version
    • in pipy
    • in GitHub
  • update the continuous testing scripts so that they are python3 only

[santoshphilip]

In release version 6.0.0

• the tutorial is not yet updated
• say this in the README.rst