ENH: interpolate/_ppform: remove unused variables
ENH: interpolate/_ppform: remove unused at_endpoint feature
ENH: interpolate: evaluate integration in PPoly + refactor the code a bit
ENH: interpolate: make c and x public attributes in PPoly
increase precision of hyperu
ENH: interpolate: add PPoly root finding
DOC: interpolate: add a warning about the power basis
BUG: interpolate: fix bug in returning object arrays from PPoly.roots + add another roots test
ENH: interpolate: add PPoly.extend that appends new intervals
Merge pull request #2724 from EvgeniBurovski/stats_refactor

refactor stats/distributions.py
ENH: interpolate: add __slots__ and a fast constructor to PPoly

Also add a sorting check to the constructor.  The fast constructor is roughly
20x faster than the default one:

In [1]: import numpy as np
In [2]: c = np.array([[1, 4], [2, 5], [3, 6]])
In [3]: x = np.array([0, 0.5, 1])
In [4]: from scipy.interpolate import PPoly
In [5]: %timeit PPoly(c, x)
10000 loops, best of 3: 20 us per loop
In [6]: %timeit PPoly.construct_fast(c, x)
1000000 loops, best of 3: 1.26 us per loop
TST: interpolate: test extending PPoly with different orders
BUG: fix moments of dweibull distribution
ENH: reenable the explicit ppf for dweibull distribution
ENH: add _stats method to dweibull distribution.

Since dweibull pdf is symmetric around origin, all odd moments
(non-central ones) are identically zero. Use this fact and
return zeros for mean and skew from _stats. For variance and kurtosis,
return Nones (and then public stats will call _munp, which
properly implemented).

Incidentally, this smokes out an assumption made by stats(): it
assumes that _stats always returns a sensible value for variance.
Fix this as well.
BUG: make generic stats filter out illegal shape parameters

This is only a partial fix:
1) not all distributions have properly vectorized _stats.
2) distributions with two or more shape parameters still fail.
TST: [stats] clean up tests a bit.
Merge pull request #2751 from juliantaylor/partition-trim

ENH: use partition for faster trim_mean
ENH: interpolate: special case low-order roots in PPoly + add a test
DEP: interpolate: deprecate ppform