A6 A7 gateway (GSM GPRS) (#195)

* init 2G gateway with SMS sending and receiving

* A6lib add

* add 2Ggateway call from setup and loop

* add schematic and image

lib/A6lib/examples/serial_relay/serial_relay.ino

@@ -0,0 +1,30 @@
+#include <A6lib.h>
+
+#ifndef ESP8266
+#define D0 0
+#define D5 8
+#define D6 7
+#endif
+
+// Instantiate the library with TxPin, RxPin.
+A6lib A6l(D6, D5);
+
+void setup() {
+    Serial.begin(115200);
+
+    delay(1000);
+
+    // Power-cycle the module to reset it.
+    A6l.powerCycle(D0);
+    A6l.blockUntilReady(9600);
+}
+
+void loop() {
+    // Relay things between Serial and the module's SoftSerial.
+    while (A6l.A6conn->available() > 0) {
+        Serial.write(A6l.A6conn->read());
+    }
+    while (Serial.available() > 0) {
+        A6l.A6conn->write(Serial.read());
+    }
+}