Catch IO::WaitReadable, too
Minor benchmark improvements
Introduce Bunny::Socket#write_nonblock_fully
Remove short-circuting, it's not entirely correct
Use #write instead of #send_raw
Add IO#write vs IO#write_nonblock synthetic benchmark

Real world results for Bunny are about the same but result of the #write
version in Bunny::Socket has less standard deviation (varies less),
so we stick to the good ol' IO#write for now.