fix(pycardium): Return when aborting

Calls to abort() shouldn't make core 1 busy-spin; call epic_exit()
instead.  Fixes #76.

Signed-off-by: Rahix <rahix@rahix.de>

pycardium/main.c

@@ -104,6 +104,11 @@ void HardFault_Handler(void)
 	epic_exit(255);
 }
 
+void _exit(void)
+{
+	epic_exit(254);
+}
+
 void gc_collect(void)
 {
 	void *sp = (void *)__get_MSP();