Implement frozen modules (#4)

pycardium/mphalport.c

 #include <stdint.h>
+#include <stdarg.h>
+#include <stdio.h>
 
 #include "py/lexer.h"
 #include "py/mpconfig.h"
@@ -29,6 +31,16 @@ void mp_hal_stdout_tx_strn(const char* str, mp_uint_t len)
 	epic_uart_write_str(str, len);
 }
 
+/* Used by MicroPython for debug output */
+int DEBUG_printf(const char *fmt, ...)
+{
+	va_list args;
+	va_start(args, fmt);
+	int ret = vprintf(fmt, args);
+	va_end(args);
+	return ret;
+}
+
 bool do_interrupt = false;
 
 /* Timer Interrupt used for control char notification */