Add method for returning cursor position in textinput

Previously, Cursor was a member on the model that did absolutely
nothing.

textinput/textinput.go

@@ -61,7 +61,6 @@ type Model struct {
 	// General settings.
 	Prompt        string
 	Placeholder   string
-	Cursor        string
 	BlinkSpeed    time.Duration
 	EchoMode      EchoMode
 	EchoCharacter rune
@@ -150,6 +149,11 @@ func (m Model) Value() string {
 	return string(m.value)
 }
 
+// Cursor returns the cursor position.
+func (m Model) Cursor() int {
+	return m.pos
+}
+
 // SetCursor moves the cursor to the given position. If the position is
 // out of bounds the cursor will be moved to the start or end accordingly.
 func (m *Model) SetCursor(pos int) {