v0.4.0

PiecewiseOrthogonalPolynomials v0.4.0

Diff since v0.3.0

Merged pull requests:

• ContinuousSpace{-1} (#58) (@dlfivefifty)
• Weighted(Jacobi(1,1)) -> Ultraspherical(-1/2) for simpler operators (#60) (@dlfivefifty)
• ArrowheadMatrix -> BBBArrowheadMatrix, use multithreading (#61) (@dlfivefifty)