Add repl.py support

Author: jepler

README.rst

@@ -133,6 +133,8 @@ Behavior
       ``code.py`` **in the REPL anymore, as the REPL is a fresh vm.** CircuitPython's goal for this
       change includes reducing confusion about pins and memory being used.
    -  After the main code is finished the REPL can be entered by pressing any key.
+      - If the file ``repl.py`` exists, it is executed before the REPL Prompt is shown
+      - In safe mode this functionality is disabled, to ensure the REPL Prompt can always be reached
    -  Autoreload state will be maintained across reload.
 
 -  Adds a safe mode that does not run user code after a hard crash or brown out. This makes it

main.c

@@ -929,6 +929,11 @@ STATIC int run_repl(safe_mode_t safe_mode) {
 
     autoreload_suspend(AUTORELOAD_SUSPEND_REPL);
 
+    if (get_safe_mode() == SAFE_MODE_NONE) {
+        const char *const filenames[] = { "repl.py" };
+        (void)maybe_run_list(filenames, MP_ARRAY_SIZE(filenames));
+    }
+
     // Set the status LED to the REPL color before running the REPL. For
     // NeoPixels and DotStars this will be sticky but for PWM or single LED it
     // won't. This simplifies pin sharing because they won't be in use when