replace zmq to cffi-rzmq for zmq 3.2
update gemspec.homepage
add dependence of ffi-rzmq to README.rdoc
update gemspec
fix bug in zmq context fini
Merge branch 'YueHonghui-master' into 20140924_merge

Conflicts:
	README.rdoc
	lib/fluent/plugin/out_zmq_pub.rb

Introduced 'bulk_send' option. If set to true, send multiple records
with the same publish key at once. Default to false.