[setup, variational] Set cython directives globally, add C compiler flags

o np.double_t -> double and Py_ssize_t -> size_t
[setup] Cythonize all .pyx files in subdirectories, ignore [clean up] build output
[mix_adapt] introduced submodule r_value and calculation of the R-value
[r_value] implemented grouping by R value
[hierarchical] fixed error message
[r_value.py] added feature ``indices``

o multivariate_r: compute the R value only for the dimensions listed in
                  ``indices``
o r_group: group only considering the R values in the dimensions listed
           in ``indices``
[GaussianInference] can now init `alpha`, `m`, `W` from a Gaussian mixture
clean up

o [hierarchical.py] replace "np.empty(self.nin) + np.inf" by
                    "np.zeros(self.nin) + np.inf" because "np.empty"
                    may produce arrays with nans (happend on my
                    machine) and nan + inf = nan but all comparisons
                    with nan involved evaluate to False
o [plot]            moved imports from 'matplotlib' inside the function
                    "plot_mixture" --> raise 'ImportError("can't import
                    matplotlib")' on call
o [setup.py]        added directive 'extras_require' --> need 'nose' for
                    testing and 'matplotlib' for plotting
[tools/regularize] Add 2D logsumexp, cythonize
[tools] Add linalg module with symmetric bilinear form, use in [variational]
[ProbabilityDensity (abstract base class)] add method `multi_evaluate`
[Gauss] cythonize and override method `multi_evaluate`
[mixture.py] override method `multi_evaluate` and cythonize
[pmc] cythonize, use multi_evaluate
[pmc] and [mixture] calculate rho only for live components

o add parameter ``componentns`` to MixtureDensity.multi_evaluate()
o use this parameter in [pmc]