The open source LWIP is broken, use espressif's liblwip.a.
Uses system_get_vdd33 instead of readvdd33.
The espressif's sdk0.9.6 beta1 (2015.02.15) release note
1、Optimize smartconfig to version v0.8；
2、Optimize AT to version 0.22.b1；
1>、Fixed bugs；
2>、Optimize the speed of transparent transmission；
3、Optimize boot to version 1.3(b3)；
1>、Fix compatibility problem of dual flash ；
4、Solve problem of the large current in deep sleep；
5、Fixed problem “check mem fail”；
6、Fixed problem of UDP socket may stop listening broadcast packet after a long time running under some special router；
7、Fixed bug related to wifi_station_scan;
8、Other optimize to make the software more reliable；
05fe3ea9f1