Add package_data to setup.py

[codecov-io]

Codecov Report

Merging #293 into master will increase coverage by 0.01%. The diff coverage is n/a.

@@            Coverage Diff             @@
##           master     #293      +/-   ##
==========================================
+ Coverage   40.21%   40.22%   +0.01%     
==========================================
  Files          86       86              
  Lines       19993    19993              
==========================================
+ Hits         8040     8042       +2     
+ Misses      11953    11951       -2

Impacted Files	Coverage Δ
ditto/metrics/network_analysis.py	48.99% <0%> (+0.21%)	:arrow_up:

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[kdheepak]

I verified that this works with a fresh environment:

$ python
Python 3.6.5 |Anaconda, Inc.| (default, Apr 26 2018, 08:42:37)
[GCC 4.2.1 Compatible Clang 4.0.1 (tags/RELEASE_401/final)] on darwin
Type "help", "copyright", "credits" or "license" for more information.
>>> from ditto.readers.gridlabd.read import Reader
>>> import ditto
>>> ditto
<module 'ditto' from '/Users/$USER/miniconda3/envs/ditto-env-py3.6/lib/python3.6/site-packages/ditto/__init__.py'>
>>>

This should resolve the first part of the issues in #292 and #287.