analogWave: add basic example

Author: facchinm

libraries/AnalogWave/examples/SineWave/SineWave.ino

@@ -0,0 +1,18 @@
+#include "analogWave.h"
+
+analogWave wave(DAC);
+
+int freq = 10;  // in hertz, change accordingly
+
+void setup() {
+  Serial.begin(115200);
+  pinMode(A0, INPUT);
+  wave.sine(freq);
+}
+
+void loop() {
+  freq = map(analogRead(A0), 0, 1024, 0, 10000);
+  Serial.println("Frequency is now " + String(freq) + " hz");
+  wave.freq(freq);
+  delay(1000);
+}