Extract and hoist net receive callbacks

This is done to avoid the accidental upval binding

docs/en/modules/net.md

@@ -135,15 +135,21 @@ Listen on port from IP address.
 
 #### Example
 ```lua
+-- server listens on 80, if data received, print data to console and send "hello world" back to caller
 -- 30s time out for a inactive client
 sv = net.createServer(net.TCP, 30)
--- server listens on 80, if data received, print data to console and send "hello world" back to caller
-sv:listen(80, function(c)
-  c:on("receive", function(c, pl) 
-    print(pl)
-  end)
-  c:send("hello world")
+
+function receiver(sck, data)
+  print(data)
+  sck:close()
+end
+
+if sv then
+  sv:listen(80, function(conn)
+    conn:on("receive", receiver)
+    conn:send("hello world")
   end)
+end
 ```
 
 #### See also
@@ -303,8 +309,8 @@ Multiple consecutive `send()` calls aren't guaranteed to work (and often don't)
 #### Example
 ```lua
 srv = net.createServer(net.TCP)
-srv:listen(80, function(conn)
-  conn:on("receive", function(sck, req)
+
+function receiver(sck, data)
   local response = {}
 
   -- if you're sending back HTML over HTTP you'll want something like this instead
@@ -315,11 +321,11 @@ srv:listen(80, function(conn)
   response[#response + 1] = "e.g. content read from a file"
 
   -- sends and removes the first element from the 'response' table
-    local function send(sk)
+  local function send(localSocket)
     if #response > 0
-        then sk:send(table.remove(response, 1))
+    then localSocket:send(table.remove(response, 1))
     else
-        sk:close()
+      localSocket:close()
       response = nil
     end
   end
@@ -328,7 +334,10 @@ srv:listen(80, function(conn)
   sck:on("sent", send)
 
   send(sck)
-  end)
+end
+
+srv:listen(80, function(conn)
+  conn:on("receive", receiver)
 end)
 ```
 If you do not or can not keep all the data you send back in memory at one time (remember that `response` is an aggregation) you may use explicit callbacks instead of building up a table like so: