Rainbows! 4.0.0 - MOAR concurrency for MOAR COARS

Rainbows! now scales to more than 1024 worker processes without
special privileges.  To enable this, Rainbows! now depends on
Unicorn 4.x and thus raindrops[1].

client_max_header_size directive is added to limit per-client
memory usage in headers.

An experimental StreamResponseEpoll concurrency option now
exists to buffer outgoing responses without any thread-safe
dependencies.  Unlike the rest of Rainbows! which works fine
without nginx, this concurrency option is /only/ supported
behind nginx, even more strongly so than Unicorn itself.
non-nginx LAN clients are NOT supported for this.  This relies
on the sleepy_penguin[2] RubyGem (and Linux).

There are some minor bug fixes and cleanups all around.  See
"git log v3.4.0.." for details.

[1] http://raindrops.bogomips.org/
[2] http://bogomips.org/sleepy_penguin/