Add scrollable form (#1)

Add scrollable form

demos/formscrollable/main.go

@@ -0,0 +1,27 @@
+// Demo code for the Form primitive.
+package main
+
+import (
+	form "github.com/name212/tview-scrollable-form"
+	"github.com/rivo/tview"
+)
+
+func main() {
+	app := tview.NewApplication()
+	form := form.NewFormScrollable().
+		AddInputField("First name", "", 20, nil, nil).
+		AddInputField("Last name", "", 20, nil, nil).
+		AddTextArea("Address", "", 40, 0, 0, nil).
+		AddDropDown("Title", []string{"Mr.", "Ms.", "Mrs.", "Dr.", "Prof."}, 0, nil).
+		AddTextView("Notes", "This is just a demo.\nYou can enter whatever you wish.", 40, 2, true, false).
+		AddCheckbox("Age 18+", false, nil).
+		AddPasswordField("Password", "", 10, '*', nil).
+		AddButton("Save", nil).
+		AddButton("Quit", func() {
+			app.Stop()
+		})
+	form.SetTitle("Enter some data").SetTitleAlign(tview.AlignLeft)
+	if err := app.SetRoot(form, true).EnableMouse(true).EnablePaste(true).Run(); err != nil {
+		panic(err)
+	}
+}