include cython in scripts and setup

o [setup.py]              added "cython" to "install_requires"
o [scripts/tidyup.sh]     delete library objects and cython associated tmp
o [scripts/build_inplace] run the build commands for python 2 and 3
[examples/variational.py] added more plots and comments
[mix_adapt/pmc] bugfix, cleanup and added Rao-Blackwell sensitive test case

o removed unneccessary definitions from pmc_test (i.e. target, sampler)
o added samples from overlapping components such that the Rao-Blackwell
  option matters
o calculate_rho_.. and application of ``mincount`` criterion separated
o during the updates perform check "weights is None" only once
[density/mixture] added support of len(MixtureDensity instance)
[pmc] avoid reapeated check (if weight==0) --> variable "live_components"
[examples] made plotting optional
[scripts/tidyup.sh] generalized deletion of *.so files
[tools/plot_test] covariances changed to test special and general case
[pmc_test] added "test_invalid_cov"
[density/mixture] removed support for iteration and item access
[tools/indicator] cover full code with test cases
[scripts] added quick_test.sh (run all tests that are not marked slow)
[examples/pmc] deleted unneccesary import
[README] Update features and dependencies
[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
[tools/regularize] Add 2D logsumexp, cythonize
[tools] Add linalg module with symmetric bilinear form
[variational] Use symmetric bilinear form
(wip) cythonize gauss and mixture's evaluate()