BUG: stub out spurious methods of Akima1DIntgerpolator

from_spline and from_bernstein_basis are inherited
from PPoly, and neither produces an Akima interpolator.
DOC: add See Also sections to Pchip and Akima interpolators
ENH: avoid repeated matrix inverse

The `sum_cov` term doesn't change, so it's faster to use a factorized version and solve.
BUG: use correct MAXGAM in beta.c

AFAICT the correct constant is used everywhere in cephes.

Also try harder to use the best order of operations when
calculating beta from gammas.
BUG: don't try to calculate beta in betainc, just call it.

fixes gh-3761
TST: sparse: add regression test for sparse matrix typemaps
BUG: sparse: fix omitted types in sparsetools typemaps

Fixes gh-3780
DOC: removed repetitive text, fixes #3782
Merge pull request #3783 from gregcaporaso/issue-3782

DOC: removed repetitive text, fixes #3782
BUG: Fix lombscargle ZeroDivisionError

Change calculation of tau to use atan2 function instead of atan.

closes gh-3787
Merge pull request #3744 from ev-br/akima_stub

stub out inherited methods of Akima1DInterpolator
Merge pull request #3781 from pv/fix-sparse-typemaps

BUG: sparse: fix omitted types in sparsetools typemaps
MAINT: update copyright notice to 2014.
MAINT: fix reST errors in integrate.quad docstring.
BUG: fix issue in scipy.special tutorial example.  Closes gh-3784.

Thanks to @CraigVD for reporting and suggestion a fix.

[ci skip]
TYPO: sheroidal -> spheroidal

Spotted this misspelling in the online docs
Merge pull request #3796 from chatcannon/doc_typo

TYPO: sheroidal -> spheroidal
Merge pull request #3791 from rgommers/doc-maint

Some maintenance for doc builds
Merge pull request #3788 from Jacobcvt12/lombscargle-atan

BUG: Fix lombscargle ZeroDivisionError
TST: lombscargle regression test related to atan vs atan2