Add button driver to drivers object
diff --git a/src/buttons.rs b/src/buttons.rs
index c360f7a..850dd11 100644
--- a/src/buttons.rs
+++ b/src/buttons.rs
@@ -17,8 +17,14 @@
     pub const SUBSCRIBE_CALLBACK: usize = 0;
 }
 
-pub fn with_callback<CB>(callback: CB) -> WithCallback<CB> {
-    WithCallback { callback }
+pub struct ButtonDriver {
+    pub(crate) _unconstructible: (),
+}
+
+impl ButtonDriver {
+    pub fn with_callback<CB>(self, callback: CB) -> WithCallback<CB> {
+        WithCallback { callback }
+    }
 }
 
 pub struct WithCallback<CB> {