update actor doc and add more actor based tests

docs/requestors.md

@@ -31,7 +31,7 @@ The cancel function, when called, should abort the in-progress work.
 ```javascript
 var fetch_data = function(callback, url) {
   $contact(function(connection) {
-    $send(connection, {get: url}, function(response) {
+    send(connection, {get: url}, function(response) {
       callback(response)
     })
   }, {host: url, port: 80})
@@ -154,11 +154,11 @@ If the requestor does not complete within the time limit, it is cancelled and th
 
 ## Requestors and Actors
 
-Requestors are particularly useful with actor messaging. Since `$send` is callback-based, it fits naturally:
+Requestors are particularly useful with actor messaging. Since `send` is callback-based, it fits naturally:
 
 ```javascript
 var ask_worker = function(callback, task) {
-  $send(worker, task, function(reply) {
+  send(worker, task, function(reply) {
     callback(reply)
   })
 }