Added support for pandas installed directly from git trunk

pandas.version == commit_hash when pandas is installed from git trunk
Use pandas.version.short_version
Make sure PeriodIndex passes through tsa. Closes #1285.
DOC: Cleanup examples folder (notebooks as default)
DOC: example remove In[] prompts
DOC: move sandox examples to incomplete examples
DOC: examples nbconvert python output template
Merge pull request #1292 from vincentarelbundock/master

DOC: cleanup examples folder and webpage
BUG/TST: Fix ARMA forecast when start == len(endog). Closes #1295
Merge pull request #1296 from jseabold/fix-predict-start-arma

BUG/TST: Fix ARMA forecast when start == len(endog). Closes #1295
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.
MAINT: Change back to path for build box