REF: ensure O(N log N) when using fft for acf

The numpy implementation will fall back to a O(N**2) version of the fft
in cases where it cannot factorize the array length, which can be a
increase in runtime of several order of magnitude. This uses the
_next_regular function from scipy to ensure that we always use array
lengths for which fftpack is optimized.
TST: add test for _next_regular

also copy the test for _next_regular from scipy
TST: Test handle_missing none keyword
ENH: Handle missing none keyword.
Merge pull request #1410 from jseabold/handle-missing-fix

ENH: Handle missing is none
TST temporarily rename tests probplot other to skip them
ENH: Make handle_data overwritable by subclasses.
Merge pull request #1416 from jseabold/handle-data-subclass

ENH: Make handle_data overwritable by subclasses.
TST: NormExpan sandbox.distributions: add basic unittests
BUG: NormExpan sandbox.distributions, no shape parameter see #1397
REF/DOC: sandbox.distribution.extras move examples to script file
DOC/REF: make example script runnable (fix imports)
REF: Let subclasses keep kwds attached to data.
Merge pull request #1417 from jseabold/handle-data-pop

REF: Let subclasses keep kwds attached to data.
Merge pull request #1403 from josef-pkt/BUG_NormExpan

BUG Bug norm expan shapes closes #1397
Merge pull request #1414 from josef-pkt/TST_probplot_other2

TST temporarily rename tests probplot-other to skip them
Memoize calculation of column widths in SimpleTable
Handle dict value in SimpleTable's format dict
Merge branch 'memoize-colwidths_rebased'

REF performance, faster SimpleTable  closes #1385 closes #1395
Fixed bug that led to wrong covariance estimator being displayed in summary