ENH: interpolate: implement spline derivatives and antiderivatives

Implement routines for computing B-splines representing derivatives and
antiderivatives of B-splines.
ENH: interpolate: add derivative+antiderivative to UnivariateSpline, too
BUG: interpolate: refuse to differentiate order 0 splines (which are not differentiable)
STY: interpolate: get rid of repeated packing/unpacking in splder
BUG: interpolate: refuse in splder to differentiate splines with too many repeated knots
DOC: interpolate: fix doc issues in splder/splantider
TST: interpolate: fix splder/splantider tests
Merge pull request #2445 from pv/splder

ENH: interpolate: implement spline derivatives and antiderivatives
DOC: stats: add nanmean, nanstd and nanmedian to the stats module-level documentation.
Merge pull request #2540 from WarrenWeckesser/doc-stats-nanfuncs

DOC: stats: add nanmean, nanstd and nanmedian to the stats module-level ...
MAINT: stats: alias the erlang to the gamma distribution.  Add gamma._sf().

Closes gh-2172 and gh-198.  See discussion on gh-2172 for details.
MAINT: stats: Modify erlang to generate a RuntimeWarning when a non-integer shape parameter is used.
Merge PR-2507 from 'rgommers/erlang-alias-to-gamma' into scipy/master.

https://github.com/scipy/scipy/pull/2507
DOC: fix error inastats. maxwell docstring and typo in stats.erlang docstring.

Closes gh-2541.
TST: Removed dependence on TestCase.
ENH: Added bool as a supporte_dtype in  sputils.
TST: Added testing of all dtypes to sum & mean methods.
TST: Made iteration over dtype data reliable in test_mean, test_sum. Added supported_dtype as attribute.
TST: Made supported_dtypes an attribute which is modified in the derived. Matrix type classes.
TST: Added bool testing to test_inv.Added bool, to CSC and CSR's supported dtypes. Added comments noting global supported dtypes.