Puma::IOBuffer is a very simple memory buffer that allows for fast
append without additional object overhead.
Additionally, turns out that IO#write on 1.9.3 is extremely
non-performant because it allows a Hash object on every invocation.
Avoid calling IO#write in a loop on 1.9.3! Use IO#syswrite if you can
(for instance when you don't care about the encoding of the output
(sockets)).
Using the work queue to communicate trimming doesn't work, it's far too
easy to starve the system doing that. Instead we now detect trimming and
work as seperate actions.