Add mqtt example

mqtt/lib/umqtt/errno.py

@@ -0,0 +1,22 @@
+EUNKNOWN=-1
+ECONCLOSE=1
+EREADLEN=2
+EWRITELEN=3
+ESTRTOLONG=4
+ERESPONSE=6
+EKEEPALIVE=7
+ENOCON=8
+ECONUNKNOWN=20
+ECONPROTOCOL=21
+ECONREJECT=22
+ECONUNAVAIBLE=23
+ECONCREDENTIALS=24
+ECONAUTH=25
+ECONNOT=28
+ECONLENGTH=29
+ECONTIMEOUT=30
+ESUBACKUNKNOWN=40
+ESUBACKFAIL=44
+STIMEOUT=0
+SDELIVERED=1
+SUNKNOWNPID=2