button: add basic button functionalities

- Provided a way to set handler for each button one-press/long-press
- Debouncing with RC filter and Schmitt trigger

src/button.h

@@ -0,0 +1,23 @@
+#ifndef __BUTTON_H__
+#define __BUTTON_H__
+
+#include "CH58x_common.h"
+
+enum keys {
+	KEY1 = 0,
+	KEY2,
+	KEY_INDEX,
+};
+
+#define KEY2_PIN (GPIO_Pin_22) // PB
+#define KEY1_PIN (GPIO_Pin_1) // PA
+
+#define isPressed(key) 		((key) ? \
+				!GPIOB_ReadPortPin(KEY2_PIN) : \
+				GPIOA_ReadPortPin(KEY1_PIN))
+
+void btn_onOnePress(int key, void (*handler)(void));
+void btn_onLongPress(int key, void (*handler)(void));
+void btn_init();
+
+#endif /* __BUTTON_H__ */