[ENH] added baseline feature to stacked graph.
pep8 compliance
Fix typos
Add stackplot baseline demo
Update changelog and whats_new
Add stackplot baseline test
Remove text from regression test output
Vectorise the loops

This boasts an O(10^4) speed up
Add docstring to example funtion

Also made a minor PEP8 change
Merge pull request #1671 from dmcdougall/feature_stack_base

Feature stack base