Added clipboard.

- Default implementation only copies to application memory. Is open for using external implementation.

ui/clipboard.go

@@ -0,0 +1,23 @@
+package ui
+
+type Clipboard interface {
+	WriteText(t string) error
+	ReadText() (string, error)
+}
+
+var DefaultClipboard Clipboard = &clipboard{}
+
+func SetClipboard(c Clipboard) { DefaultClipboard = c }
+
+type clipboard struct {
+	value string
+}
+
+func (c *clipboard) WriteText(t string) error {
+	c.value = t
+	return nil
+}
+
+func (c *clipboard) ReadText() (string, error) {
+	return c.value, nil
+}