add Module and BaseModule. Closes #1

module.go

@@ -0,0 +1,16 @@
+package alice
+
+// Module is a marker interface for structs that defines how to initialize instances.
+type Module interface {
+	// IsModule indicates if this is a module.
+	IsModule() bool
+}
+
+// BaseModule is an implementation of Module interface. It should be embeded into each module defined in the
+// application.
+type BaseModule struct{}
+
+// IsModule indicates it is a module.
+func (b *BaseModule) IsModule() bool {
+	return true
+}

module_test.go

@@ -0,0 +1,12 @@
+package alice
+
+import (
+	"testing"
+)
+
+func TestBaseModule(t *testing.T) {
+	var base Module = &BaseModule{}
+	if !base.IsModule() {
+		t.Error("BaseModule is expected to be a Module, but it is not")
+	}
+}