remove RubyForge and Freecode references

Both sites are gone.
remove mongrel.rubyforge.org references

mongrel.rubyforge.org has been dead longer than rubyforge.org!
http: remove the keepalive requests limit

This was a hack for some event loops such as those found in nginx
and some Rainbows! concurrency models.  Using epoll/kqueue with
one-shot notification (which yahns does) avoids all fairness
problems.
http: reduce parser from 72 to 56 bytes on 64-bit

This allows the parser struct to fit in one cache line on
x86-64 systems where cache lines are 64 bytes.

Using 32-bit integer lengths is safe here because these are only for
tracking offsets within the HTTP header buffer.  We can safely limit
HTTP headers and in-memory buffers to be less than 4GB without
anybody complaining.

HTTP bodies continue to use off_t (usually 64-bit, even on 32-bit
systems) sizes and support as much as the OS/hardware can handle.
examples: add run_once to before_fork hook example

There may be code in a before_fork hook which should run only once,
document an example using a guard variable since it may not be
immediately obvious to all users.

Inspired-by: Bráulio Bhavamitra <braulio@eita.org.br>

http://bogomips.org/unicorn-public/m/20141004015707.GA1951@dcvr.yhbt.net.html