math/py-pandas: 0.17.0 -> 0.18.1

Changes:

http://pandas.pydata.org/pandas-docs/version/0.18.1/

• Add optional dependencies on devel/py-Jinja2 and textproc/py-xlsxwriter

PR: 209521
Submitted by: John W. O'Brien <john@saltant.com> (maintainer)