ENH: stats: Add the power_divergence function that generalizes the
chi-squared test statistic, and allow it to be used in chi2_contingency.
BUG: interpolate: ensure fitpack work arrays are aligned to double boundaries

gfortran on some optimization levels (-O3) assumes that double-precision
arrays are aligned in memory on sizeof(double) boundaries.

The fitpack_surfit routine failed to properly ensure this, which results
to crashes in some cases.

Fixes gh-1310
TST: interpolate: add regression test for gh-1310
Merge pull request #2559 from WarrenWeckesser/stats-chisquare-gtest

ENH: stats: Add the power_divergence function that generalizes the chi-squared test statistic, and allow it to be used in chi2_contingency.
Merge pull request #2698 from pv/fix-1310

 BUG: interpolate: ensure fitpack work arrays are aligned to double boundaries
BF: fix error saving zero entries in sparse matrix

I assumed obj.size was the same as np.prod(obj.shape), but this isn't so
for sparse matrices.  Fix and test.

Closes gh-2700
Merge pull request #2701 from matthew-brett/empty-sparse-fix

BUG: io: fix error saving zero entries in sparse matrix
MAINT: stats: Removed obfuscatory alias for 'vectorize' from distributions.py