Update comments for code review

Author: fahhem

platform/mbed_retarget.cpp

@@ -228,7 +228,7 @@ extern "C" FILEHANDLE PREFIX(_open)(const char* name, int openmode) {
 
     FileHandle *res = NULL;
 
-    /* FILENAME: ":0x12345678" describes a FileHandle* */
+    /* FILENAME: ":(pointer)" describes a FileHandle* */
     if (name[0] == ':') {
         void *p;
         memcpy(&p, name + 1, sizeof(p));
@@ -826,6 +826,7 @@ void mbed_set_unbuffered_stream(std::FILE *_file) {
  */
 std::FILE *mbed_fdopen(FileHandle *fh, const char *mode)
 {
+    // This is to avoid scanf(buf, ":%.4s", fh) and the bloat it brings.
     char buf[2 + sizeof(fh) + 1]; /* :(pointer) + null byte */
     static_assert(sizeof(buf) == 7, "Pointers should be 4 bytes.");
     buf[0] = ':';