Add libesphttpd to extras and supporting example (#458)

* libesphttpd: added extras and example

* Added "heatshrink" as a submodule

* Updated libesphttpd

* Updated libesphttpd

* Trying to fix the commit id

* Updated libesphttpd

* Added zlib1g-dev package

* Use native gcc to build mkespfsimage and mkupgimg

* Added NS and GW for DHCP server configuration

examples/esphttpd/cgi.h

@@ -0,0 +1,10 @@
+#ifndef CGI_H
+#define CGI_H
+
+#include <libesphttpd/httpd.h>
+
+int cgiLed(HttpdConnData *connData);
+int tplLed(HttpdConnData *connData, char *token, void **arg);
+int tplCounter(HttpdConnData *connData, char *token, void **arg);
+
+#endif