COMPAT: Repair PY2 issues

[addisonlynch]

Merging 0.7.4 py2 compat changes into master in prep for 0.8.0

• closes Not working with new pandas versions #665
• tests added / passed
• passes git diff upstream/master -u -- "*.py" | flake8 --diff
• added entry to docs/source/whatsnew/vLATEST.txt

[bashtage]

The important question is whether pdr should be Python 3 only for 0.8 on, in which case all of the PY2/3 compat code can be removed

[addisonlynch]

I think that Python 3 only would be sensible given that this package spun out of pandas, which ended py2 support. I dont think the 10-15% of pdr userbase which is 2.6/7 warrants keeping it around long enough, and even if so, for how long should it last?

[bashtage]

Either 0.8 is the last PY2 compat release of 0.7 is the last PY2 release. If it is the latter, then we can remove all PY2/3 code now.

[addisonlynch]

Maybe keep for 0.8, end in 0.9...thinking it could be a little quick to cut it out (without prior notification) if 0.8 is released soon. We already have the code here, so not much work to keep it around.

[addisonlynch]

Looks like one pd.compat.binary_type was missed in moex.py. Added that fix here as well. This will now close #665

[bashtage]

Need to add 3.7 for testing and get tests/xfail before release.

[gliptak]

With build green, could 0.8.0pre be tagged?

[bashtage]

I think docs need to be updated before the tag, but close.

[bashtage]

FWIW current master is now correctly tagged 0.8.0dev0