ENH: Add seasonal plotting.
TST: Add test for seasonality plots.
DOC: Add example to docstring
DOC: Add seasonality plots to graphics docs.
RLS: Add note about seasonality plots to release notes
DOC: Add plot to docstring.
Merge pull request #1290 from jseabold/tsa-plots

ENH: Add seasonal plotting functions.
TST: Update hard-coded path.
Merge pull request #1305 from jseabold/update-gretl-script

TST: Update hard-coded path.