ENH: Add ext parameter to UnivariateSpline call

Pass parameter to fitpack.splev to control how to handle out of range
evaluations. Added test to scipy/interpolate/tests/test_fitpack2.py.

See ticket 3557.

closes gh-3557
STY avoid unnecessary transposes in csr_matrix.getcol/row
ENH: Add ext parameter to UnivariateSpline

Pass parameter to fitpack.splev to control how to handle out of range
evaluations. Parameter ext can be passed via __init__ or __call__. Added
test to scipy/interpolate/tests/test_fitpack2.py. Tests if UnivariateSpline
call equals x ** 3 for out of range x and extrapolation modes 0 and 1.

See ticket 3557.

closes gh-3557
ENH: Add ext parameter to UnivariateSpline

Pass parameter to fitpack.splev to control how to handle out of range
evaluations. Parameter ext can be passed via __init__ or __call__. Added
test to scipy/interpolate/tests/test_fitpack2.py. Tests if UnivariateSpline
call equals x ** 3 for out of range x and extrapolation modes 0 and 1.
Modify _from_tck, derivative, and antiderivative methods to use ext
parameter. __init__ of LSQUnivariateSpline and InterpolatedUnivariateSpline
now accept ext.

See ticket 3557.

closes gh-3557
BUG: Removed unnecessary storage of args as instance variables in Rbf
DOC: Savitzky-Golay filter version added
DOC: move versionadded to notes
DOC: write in complete sentences and move versionadded in docstrings
TST: add tests for ext parameter of {Interpolated,LSQ}UnivariateSpline

Light smoke tests only.
ENH: interpolate: string keywords to control extrapolation in fitpack2

splev accepts ext=0, 1, 2; class-based wrappers take `ext` as either
int, or a string value.
DOC: typos in BPoly docstring

[ci skip]
DOC: add a note about the sign of the shape parameter to genextreme.

closes gh-3844, closes gh-1851

[ci skip]
Merge pull request #3879 from ev-br/interp_docs

Small tweaks to the docs:

  -  fix a typo in BPoly docstrings
  -  add to the docstring of genextreme a cautionary note about the sign of the shape parameter.
Merge pull request #3878 from argriffing/move-versionadded

DOC: move versionadded to notes
Merge pull request #3877 from argriffing/savgol-version-added

DOC: Savitzky-Golay filter version added
Merge pull request #2 from ev-br/pr-3773_

Pr 3773
Merge pull request #3773 from Jacobcvt12/UnivariateSpline

ENH: Add ext parameter to UnivariateSpline call
Merge pull request #3861 from jetuk/master

BUG: Removed unnecessary storage of args as instance variables in Rbf
Merge pull request #3772 from jnothman/simplify-csc-getcol

STY avoid unnecessary transposes in csr_matrix.getcol/row