Updated for zmq 3.2
Rearrange as a Hoe project, add some specs

--HG--
rename : zmq.gemspec => Rakefile
rename : extconf.rb => ext/zmq/extconf.rb
rename : rbzmq.c => ext/zmq/zmq.c
Fix a few things in the extension.

* Correct argument ordering for zmq_msg_{recv,send}.
* Rename ZMQ.version to ZMQ.zeromq_version to disambiguate
  it from the gem version.
Checkpoint: add more specs
Fix return-code check to be compatible with 3.x.

Also modify the error-checking to only raise ZMQ::Errors
on zmq-specific errors. All others use rb_sys_fail() so
they're rescuable. EAGAIN errors no longer return +nil+;
they are raised as Error::EAGAIN so non-blocking code
can handle the case via poll+retry.
Add .rvmrc and gemset