BUG: special: reimplement struve functions in C
GEN: special: regenerate files
special/struve: fix negative z
special/struve: take underflowing bessel functions into account in bessel series error estimate
special/struve: try to postpone under/overflows in power series
special/struve: fix struve L overflow handling
special/struve: deal with breakdown of the asymptotic expansion
special/struve: fix convergence criterion of power series

For v < 0, |v| >> 1, the summand may start to increase again for n > v,
so push the convergence point far enough.
special/struve: update comments
special/struve: fix c++ style comments
BUG: special: add asymptotic expansions to shichi

Enable also the si+ci tests, they seem to work.
Spell Smirnov's name properly.
Remove spurious EOL and EOF whitespace.
BUG: stats: The formula for the skew in poisson.stats() was incorrect--it did not take the sqrt.
BUG: levene didn't sort before trimming closes #2555
TST: Silence some warnings.
TST: Small test optimizations.
TST: Add warning catches for indexing and inv and exp tests.
TST: Add warning catches to tests in sparse.linalg.
TST: remove duplicate with-statement in sparse/tests/test_base.py