Update init.lua example to use new wifi.sta.config() implementation (#1953)

* Update init.lua example in upload.md with new station config format
* Fixed typo in description of wifi.eventmon.register()
* Fixed typo and improved example init.lua in docs/en/upload.md

docs/en/modules/wifi.md

@@ -1504,7 +1504,7 @@ T: Table returned by event.
 - `wifi.eventmon.STA_DISCONNECTED`: Station was disconnected from access point.  
 	- `SSID`: SSID of access point.  
 	- `BSSID`: BSSID of access point.  
-	- `REASON`: See [wifi.eventmon.reason](#wifieventmonreason) below.  
+	- `reason`: See [wifi.eventmon.reason](#wifieventmonreason) below.  
 - `wifi.eventmon.STA_AUTHMODE_CHANGE`: Access point has changed authorization mode.    
 	- `old_auth_mode`: Old wifi authorization mode.  
 	- `new_auth_mode`: New wifi authorization mode.  

docs/en/upload.md

@@ -56,24 +56,65 @@ function startup()
     end
 end
 
-print("Connecting to WiFi access point...")
-wifi.setmode(wifi.STATION)
-wifi.sta.config(SSID, PASSWORD)
--- wifi.sta.connect() not necessary because config() uses auto-connect=true by default
-tmr.create():alarm(1000, tmr.ALARM_AUTO, function(cb_timer)
-    if wifi.sta.getip() == nil then
+-- Define WiFi station event callbacks 
+wifi_connect_event = function(T) 
+  print("Connection to AP("..T.SSID..") established!")
   print("Waiting for IP address...")
-    else
-        cb_timer:unregister()
-        print("WiFi connection established, IP address: " .. wifi.sta.getip())
-        print("You have 3 seconds to abort")
+  if disconnect_ct ~= nil then disconnect_ct = nil end  
+end
+
+wifi_got_ip_event = function(T) 
+  -- Note: Having an ip address does not mean there is internet access!
+  -- Internet connectivity can be determined with net.dns.resolve().    
+  print("Wifi connection is ready! IP address is: "..T.IP)
+  print("Startup will resume momentarily, you have 3 seconds to abort.")
   print("Waiting...") 
   tmr.create():alarm(3000, tmr.ALARM_SINGLE, startup)
 end
-end)
-```
 
-Inspired by [https://github.com/ckuehnel/NodeMCU-applications](https://github.com/ckuehnel/NodeMCU-applications)
+wifi_disconnect_event = function(T)
+  if T.reason == wifi.eventmon.reason.ASSOC_LEAVE then 
+    --the station has disassociated from a previously connected AP
+    return 
+  end
+  -- total_tries: how many times the station will attempt to connect to the AP.
+  local total_tries = 75
+  print("\nWiFi connection to AP("..T.SSID..") has failed!")
+
+  --There are many possible disconnect reasons, the following iterates through 
+  --the list and returns the string corresponding to the disconnect reason.
+  for key,val in pairs(wifi.eventmon.reason) do
+    if val == T.reason then
+      print("Disconnect reason:"..val.."("..key..")")
+      break
+    end
+  end
+
+  if disconnect_ct == nil then 
+    disconnect_ct = 1 
+  else
+    disconnect_ct = disconnect_ct + 1 
+  end
+  if disconnect_ct < total_tries then 
+    print("Retrying connection...(attempt "..(disconnect_ct+1).." of "..total_tries..")")
+  else
+    wifi.sta.disconnect()
+    print("Aborting connection to AP!")
+    disconnect_ct = nil  
+  end
+end
+
+-- Register WiFi Station event callbacks
+wifi.eventmon.register(wifi.eventmon.STA_CONNECTED, wifi_connect_event)
+wifi.eventmon.register(wifi.eventmon.STA_GOT_IP, wifi_got_ip_event)
+wifi.eventmon.register(wifi.eventmon.STA_DISCONNECTED, wifi_disconnect_event)
+
+print("Connecting to WiFi access point...")
+wifi.setmode(wifi.STATION)
+wifi.sta.config({ssid=SSID, pwd=PASSWORD, save=true})
+-- wifi.sta.connect() not necessary because config() uses auto-connect=true by default
+
+```
 
 # Compiling Lua on your PC for Uploading