BUG: signal: Use np.linspace instead of np.arange to fix an off-by-one error that could occur in dstep and dimpulse.
MAINT: to support older versions of numpy, use scipy.special.p_roots instead of np.polynomial.legendre.leggauss
Merge pull request #2663 from WarrenWeckesser/bug-dstep-dimpulse

BUG: signal: Use np.linspace instead of np.arange to fix an off-by-one error that could occur in dstep and dimpulse.
Merge pull request #2676 from argriffing/logm-p-roots

MAINT: to support older versions of numpy, use scipy.special.p_roots ins...