Restructure following https://github.com/fogleman/nes ideas

gb/console.go

@@ -0,0 +1,17 @@
+package gb
+
+type Console struct {
+	Cartridge *Cartridge
+}
+
+func NewConsole(path string) (*Console, error) {
+	cartridge := InsertCartridge(path)
+
+	console := Console{cartridge}
+
+	return &console, nil
+}
+
+func (console *Console) Update(dt uint64) {
+	console.StepSeconds(dt)
+}