mac OS displays free space as MB and set creation time to more appropriate date

[ptorrone]

on a mac (os 10.11.6) metro express will show up with 48KB, 39.3 MB free. also, the time volume (partition create time/date) is "Wednesday, December 31, 1969 at 7:00 PM" ... we could pick a more appropriate date.

running - 1.8.5-20161020 on 2016-10-20 Adafruit Feather M0 Basic with samd21g18

image attached.

[tannewt]

File size is now correct. I'm not going to change creation time because we're going to format the fs externally rather than using MicroPython to do it.