MAINT: remove underscore from _GenericKDE name.
MAINT: rename Reg, CensoredReg --> KernelReg, KernelCensoredReg.
MAINT: deprecate nonparametric.KDE, new name is KDEUnivariate.

Also improve its docstring, add example.
DOC: describe contents of nonparametric module.
TST: fix precision issues in nonparametric tests.

The match with R is slightly worse now, but in most cases still matching to
~1% for bw estimation.  Since the differences beween cv_ls, cv_ml and rules of
thumb can be over 50%, this mismatch is not relevant.

One of the tests needs to be fixed; marginal effects tests seem to still need
some work too.  That's for later.
MAINT: address review comments from Josef on PR-562.
Merge branch 'nonparametric', GSOC George/Ralph, closes #562
DOC: adjust example to use joblib
DOC: change example in sandbox try_smoothers.py
DOC: add kernel_regression example scripts
REF/BUG: add W in KernelCensoredReg, add example with random censoring
DOC for BUG: example bw='aic' first bw is negative and too small in absolute terms
ENH: add sortindex so we can reverse sorting
ENH: dgp_examples, some example functions and processes
ENH: improve nonparametric/dgp_examples with script
REF: remove original class, now obsolete
DOC: move examples out of dgp_example
DOC: docstrings dgp_examples
ENH: add example from ex_kernel_regression3 to dgp, add heteroscedasticity
REF: rename dgp base class, add seed in example