ENH: convert the cryptically named scipy.special information theory functions into ufuncs
TST: add negative values to scipy.special information theory function tests
DOC: improve scipy.special information theory ufunc docstrings
MAINT: add .pxd files
MAINT: simplify kl_div
MAINT: combine multiple ufuncs into the same .pxd file
ENH: add huber loss function to the collection of convexity-related ufuncs
PEP8: pacify the pep8 overseer
ENH: add pseudo-huber loss function ufunc
BUG: stats: correct value of powerlaw.logpdf(0, 1) is 0. Closes gh-3986.
BUG: stats: Better handling of x=0 in the 'exponpow' distribution.

exponpow.logpdf(0, 1) now returns 0.0 instead of nan.

When b < 1, exponpow.pdf(0, b) and exponpow.logpdf(0, b) now
return inf instead of nan.

Closes gh-3982.
BUG: stats: gengamma.pdf(0,1,1) now returns 1.0 instead of nan.

Closes gh-3985.
DOC: stats: Maintenance work on the distribution docs in the stats tutorial.

* Added links to implementations in the list of distributions in the tutorial.
* Removed distributions from the .rst files that are not implemented in scipy:
    continuous.rst:
        Doubly Non-central F
        Doubly Non-central t
        Noncentral beta
        Noncentral chi
        Studentized Range
        Symmetric Power
        Wishart
        Student Z
    discrete.rst
        Discete Gaussian
* Fixed spelling of "Saunders" in "Birnbaum-Saunders".
* Removed extraneous blank lines.
DOC: stats: Maintenance work on the distribution docs in the stats tutorial.

Created a separate .rst file for each distribution.
DOC: stats: Fix whitespace in the LaTeX formulas of some distributions.
DOC: stats: Remove extraneous LaTeX brackets from discrete.rst.
Merge pull request #4000 from WarrenWeckesser/stats-powerlaw-nan

BUG: stats: Fix edge-case handling in a few distributions.
Merge pull request #4008 from WarrenWeckesser/doc-split-distr

DOC: stats: Split the descriptions of the distributions in the tutorial into separate files.
Merge pull request #3981 from argriffing/infotheory-ufuncs

turn the cryptically named scipy.special information theory functions into ufuncs