Rewrite init app in C, introduce MSL (MOP3 System Library)

libmsl/init/__premain.c

@@ -0,0 +1,22 @@
+#include <stdint.h>
+#include <m/proc.h>
+
+extern volatile uint8_t __bss_start[];
+extern volatile uint8_t __bss_end[];
+
+extern void app_main (void);
+
+static void msl_clear_bss (void) {
+  uint8_t *p = (uint8_t*)__bss_start;
+  while (p < __bss_end) {
+    *p++ = 0;
+  }
+}
+
+void __premain (void) {
+  msl_clear_bss ();
+
+  app_main ();
+
+  m_proc_quit ();
+}