Rainbows! 2.1.0 - Cool.io, bugfixes and more!

Cool.io (new version of Rev) support is explicitly added
(it always worked before).  ":Coolio" may be used in place
of ":Rev" anywhere in your Rainbows! config file.

There is a new "keepalive_requests" config directive to limit
the number of requests a single connection may make (default:
100, same as nginx).  This may be useful for better
load-balancing characteristics.

The old "Rev" prefixes remain supported as long as Cool.io
remains compatible with Rev (likely forever).

Bug fixes:

* Rainbows::ThreadTimeout middleware with multiple clients
* large, pipelined upload errors with Revactor+Coolio(Rev)
* high CPU usage for maintaining idle keepalive on *Fiber*
* needless ThreadPool wakeups
* request env prematurely cleared keepalive requests,
  breaking some middlewares such as Clogger.
* "close" not called on body if wrapper and sendfile used together

Various code cleanups, and our RDoc website is JavaScript-free.
See the ChangeLog or git for all changes.