Add sub-modules to 'zmq' module's table.

src/poller.lua

@@ -92,5 +92,6 @@ function M.new(pre_alloc)
 	}, poller_mt)
 end
 
+zmq.poller = M
 return setmetatable(M, {__call = function(tab, ...) return M.new(...) end})
 

src/threads.lua

@@ -108,4 +108,5 @@ function M.get_parent_ctx(ctx)
 	return parent_ctx
 end
 
+zmq.threads = M
 return M