pysat v3.X compatibility

[rstoneback]

Description

Addresses #

Includes bug fixes for new versions of pandas and pysat. Further, tweaks setup.py for greater robustness.

Type of change

Please delete options that are not relevant.

• Bug fix (non-breaking change which fixes an issue)

How Has This Been Tested?

Unit tests

Test Configuration:

• MacOS 10.15.4
• Python 3.7.2

Checklist:

• Make sure you are merging into the develop (not master) branch
• My code follows the style guidelines of this project
• I have performed a self-review of my own code
• I have commented my code, particularly in hard-to-understand areas
• I have made corresponding changes to the documentation
• My changes generate no new warnings
• I have added tests that prove my fix is effective or that my feature works
• New and existing unit tests pass locally with my changes
• Any dependent changes have been merged and published in downstream modules
• Add a note to CHANGELOG.md, summarizing the changes

[rstoneback]

Tested on local system. Travis CI checks aren't being activated at the moment for some reason.