Add basic HID keyboard support

src/lib/util.h

@@ -17,3 +17,8 @@ typedef uint64_t exit_code_t;
 #define EXIT_CODE_OK 0
 #define EXIT_CODE_NOT_FOUND ((uint64_t)-2)
 #define EXIT_CODE_GENERAL_FAILURE ((uint64_t)-1)
+
+static inline void sleep(uint64_t ms) {
+  for (volatile uint64_t i = 1000000 * ms; i; i--) // Very approximately
+    ;
+}