Adds a rank size plot to inequality

[jstac]

Generates a rank size plot from supplied data. This is quite useful and the code has been written to avoid new external dependences.

No test and I don't have time to write one now. Would appreciate if we can merge this subject to review and then think about proper tests later.

[pep8speaks]

Hello @jstac! Thanks for updating this PR. We checked the lines you've touched for PEP 8 issues, and found:

• In the file quantecon/__init__.py:

Line 10:1: W191 indentation contains tabs
Line 11:1: W191 indentation contains tabs
Line 30:1: W191 indentation contains tabs
Line 42:80: E501 line too long (81 > 79 characters)
Line 43:1: W191 indentation contains tabs

• In the file quantecon/inequality.py:

Line 150:80: E501 line too long (80 > 79 characters)
Line 156:1: W391 blank line at end of file

Comment last updated at 2019-12-08 23:10:10 UTC

[coveralls]

Coverage decreased (-0.1%) to 93.952% when pulling 64a16f1 on add_rank_size into ad70e0e on master.

[mmcky]

thanks @jstac this looks great.