tools/mpremote: Add mkdir and rmdir to RemoteFS.
tools/mpremote: Add mkdir and rmdir to RemoteFS.

This allows the remote MicroPython instance to create and delete
directories from the mounted host filesystem in addition to the already
existing functionality of reading, creating, and modifying files.

Signed-off-by: Michael Bentley <7887d06feac506c5c160db6d71f2063861063ad4@gmail.com>

adafruit/circuitpython,adafruit/circuitpython,adafruit/circuitpython,adafruit/circuitpython,adafruit/circuitpython,adafruit/circuitpython