Client driver for WiFiNINA firmware (#98)

* wifinina: implementation of WiFiNINA driver, including:
   - TCP client example is working
   - reading sockets and mqtt working
   - switched over to common net package also used by espat package
   - smoke tests and updated README for wifinina

wifinina/timer.go

@@ -0,0 +1,28 @@
+package wifinina
+
+import "time"
+
+func wait(duration time.Duration) {
+	newTimer(duration).WaitUntilExpired()
+}
+
+type timer struct {
+	start    int64
+	interval int64
+}
+
+func newTimer(interval time.Duration) timer {
+	return timer{
+		start:    time.Now().UnixNano(),
+		interval: int64(interval),
+	}
+}
+
+func (t timer) Expired() bool {
+	return time.Now().UnixNano() > (t.start + t.interval)
+}
+
+func (t timer) WaitUntilExpired() {
+	for !t.Expired() {
+	}
+}