io: rework io.popen to use posix_spawn()

..and accept 'rw' flag to make reading _and_
writing to the process' stdin and stdout possible.
io: add io.streamfile()
http.server: smarter res:add()
io: flush file input buffer on seek
README: add chat server example
README: refer to the example
io: skip empty strings in write methods
io: fix empty string skipping code
parsers: fix stack overflow
fix compilation with EV_MULTIPLICITY set
queue: add blocking multiple producer/consumer queue
lem: use reguler ints for queue indexes
io: fix memory leak on error in io.popen()
io: return stream, pid from io.popen()
http.client: added
set EV_SIGNAL_ENABLE and EV_CHILD_ENABLE

to prepare for upcoming signal library
and reap child processes even when
EV_CHILD_ENABLE is not set
Merge branch 'master' of git://github.com/esmil/lem