Add a generic way to deserialize a flatbuffer in Go.

Similar to what protobufs does with its `Message` interface, introduce here such interface and create a generic `GetRootAs` method to deserialize a flatbuffer.

go/lib.go

@@ -0,0 +1,13 @@
+package flatbuffers
+
+// FlatBuffer is the interface that represents a flatbuffer.
+type FlatBuffer interface {
+	Table() Table
+	Init(buf []byte, i UOffsetT)
+}
+
+// GetRootAs is a generic helper to initialize a FlatBuffer with the provided buffer bytes and its data offset.
+func GetRootAs(buf []byte, offset UOffsetT, fb FlatBuffer) {
+	n := GetUOffsetT(buf[offset:])
+	fb.Init(buf, n+offset)
+}