tools/mpremote: Add repl option to escape non-printable characters.

This commit adds the "--escape-non-printable" option to the repl command.
When specified the REPL console will escape non-printable characters,
printing them as their hex value in square brackets.

This escaping behaviour was previously the default and only behaviour, but
it is now opt-in.

As part of this change, the speed of echoing device data to the console is
improved by by reading and writing in chunks.

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

docs/reference/mpremote.rst

@@ -92,6 +92,7 @@ The full list of supported commands are:
 
   Options are:
 
+  - ``--escape-non-printable``, to print non-printable bytes/characters as their hex code
   - ``--capture <file>``, to capture output of the REPL session to the given
     file
   - ``--inject-code <string>``, to specify characters to inject at the REPL when