finish AppSink impl and add example

examples/common.go

@@ -0,0 +1,23 @@
+package examples
+
+import (
+	"fmt"
+
+	"github.com/tinyzimmer/go-gst/gst"
+)
+
+// Run is used to wrap the given function in a main loop and print any error
+func Run(f func() error) {
+	mainLoop := gst.NewMainLoop(gst.DefaultMainContext(), false)
+
+	defer mainLoop.Unref()
+
+	go func() {
+		if err := f(); err != nil {
+			fmt.Println("ERROR!", err)
+		}
+		mainLoop.Quit()
+	}()
+
+	mainLoop.Run()
+}