feature(udp_router): add customizable udp router

rebar.config

@@ -32,6 +32,10 @@
                   "examples/udp"
                  ]}.
 
+{deps,
+    [ {gproc, {git, "https://github.com/uwiger/gproc", {tag, "0.8.0"}}}
+    ]}.
+
 {cover_enabled, true}.
 {cover_opts, [verbose]}.
 {cover_export_enabled, true}.

src/udp_router/doc/router.plantuml

@@ -0,0 +1,43 @@
+@startuml
+skinparam dpi 300
+left to right direction
+
+frame client {
+      card clinet1
+      card client2
+      card client3
+}
+
+frame router {
+      label "router converts the udp connection\nto long connection in the application"
+      agent router1
+      agent router2
+      agent router3
+}
+
+frame connection {
+      card connection1
+      card connection2
+      card connection3
+}
+
+clinet1 .[#red].> router1
+client2 .[#blue].> router1
+client3 ..> router2
+client3 ..> router3
+
+router1 -[#red]-> connection1 : client1
+router1 -[#blue]-> connection2 : client2
+router2 --> connection3 : client3
+router3 --> connection3 : client3
+
+note bottom of router1
+different clients use the same UDP channel,e.g NAT
+endnote
+
+
+note right of router
+router2 and router3 are multiple channels used by a client,e.g LB
+endnote
+
+@enduml