ENH: interpolate: BSpline

Add a base class BSpline, and a low-level cython routines
for evaluating b-spline functions. This class only evaluates
b-splines and does not do any fitting. Representation is
compatible with FITPACK.
ENH: interpolate: interpolating BSplines

Add a routine for constructing an interpolating spline
given data. Accepts knots for interpolation. If not supplied,
selects knots automatically. Handles fixed values of derivatives
at boundaries. All linear algebra is banded, so that memory
footprint should be reasonable.
DEP: interpolate: deprecate splmake and friends

Use make_interp_spline and BSpline in interp1d instead.
MAINT: bsplines: reuse _deBoor_D from __fitpack

This improves performance over a homemade evalution routine, making
it comparable to fitpack in performance.
BUG: interpolate: fix an indexing bug in __fitpack.h:_deBoor_D

a typo (m vs n), shows up when doing derivatives of splines with
multiple knots