Create buttons module

Temporarily just logging button presses, as alarms module doesn't yet
exist.

components/buttons/buttons.h

@@ -0,0 +1,16 @@
+/*
+ * SPDX-License-Identifier: AGPL-3.0-only
+ * Copyright (c) Camden Dixie O'Brien
+ */
+
+#ifndef BUTTONS_H
+#define BUTTONS_H
+
+typedef void (*ButtonCallback)(void);
+
+/**
+ * Initialize the buttons module.
+ */
+void buttons_init(void);
+
+#endif