tools/mpremote: Make RemoteFile objects iterable.

So that filesystems mounted with "mpremote mount" can have their files
iterated over, making them consistent with other files.

Signed-off-by: Damien George <damien@micropython.org>

tools/mpremote/mpremote/pyboardextended.py

@@ -143,6 +143,15 @@ def __enter__(self):
     def __exit__(self, a, b, c):
         self.close()
 
+    def __iter__(self):
+        return self
+
+    def __next__(self):
+        l = self.readline()
+        if not l:
+            raise StopIteration
+        return l
+
     def ioctl(self, request, arg):
         if request == 1:  # FLUSH
             self.flush()