raindrops 0.19.1

This release fixes some warnings on newer Rubies.

We're no longer on bogomips.org since it's due
for expiry and I can't pay extortionists for a .org, so
s/bogomips.org/yhbt.net/ for now, and be prepared to move again
when extortionists move onto extorting the .net TLD.

      doc: switch homepage to dark216
      ext/raindrops/extconf: fix cflags reset on ancient CC
      fixes for newer rubies
      replace bogomips.org with yhbt.net