eliminate most sync.Pool use, gives a safer but slightly slower interface

src/yggdrasil/pool.go

@@ -0,0 +1,20 @@
+package yggdrasil
+
+import "sync"
+
+// Used internally to reduce allocations in the hot loop
+//  I.e. packets being switched or between the crypto and the switch
+// For safety reasons, these must not escape this package
+var pool = sync.Pool{New: func() interface{} { return []byte(nil) }}
+
+func pool_getBytes(size int) []byte {
+	bs := pool.Get().([]byte)
+	if cap(bs) < size {
+		bs = make([]byte, size)
+	}
+	return bs[:size]
+}
+
+func pool_putBytes(bs []byte) {
+	pool.Put(bs)
+}