all: Use the name MicroPython consistently in comments

There were several different spellings of MicroPython present in comments,
when there should be only one.
diff --git a/esp8266/esp_mphal.c b/esp8266/esp_mphal.c
index 55f9a58..61848fd 100644
--- a/esp8266/esp_mphal.c
+++ b/esp8266/esp_mphal.c
@@ -1,5 +1,5 @@
 /*
- * This file is part of the Micro Python project, http://micropython.org/
+ * This file is part of the MicroPython project, http://micropython.org/
  *
  * The MIT License (MIT)
  *