Make Python 2 compatible

thanks to @ltalirz

• pyIAST is now compatible with Python 2
• an up-to-date version of pandas is required and argmin is changed to idxmin
• the code is now better-formatted with yapf

Make release consistent with PyPI

no changes since last; just making the release "1.4.2" consistent with PyPI.

TemkinApprox fixed

The TemkinApprox isotherm formula was missing a -1 term. The TempkinApprox isotherm and test was updated to fix this bug.

v1.3

Having problems with PyPI. This version is consistent with the manuscript.

pyIAST_v1.1

This release is consistent with the manuscript:

C. Simon, B. Smit, M. Haranczyk. pyIAST: Ideal Adsorbed Solution Theory (IAST) Python Package. Computer Physics Communications. (2015) DOI