BUILD: Always import setuptools (e.g. for develop)
ENH: Added pure Python Kalman filter
FIX: `cov_params` side effects on `Model` matrices
CLEAN: Improved gitignore
DOC: Added user guide to LaTeX output.
DOC: remove misleading note about Cython policy.
ENH: Added support for iPython notebooks in Sphinx
DOC: Comprehensive state space doc improvements.