Merge pull request adafruit#1649 from dhalbert/reload-flush-filesystem

flush filesystem before resetting heap

Merge pull request adafruit#1648 from tannewt/board_i2c_crash

Long live shared bus singletons

Merge pull request adafruit#1620 from dhalbert/display-transactions-fix

Rework displayio display bus transaction handling during refresh

Merge pull request adafruit#1519 from tannewt/speed_debug

Add fast seek support and turn on auto brightness by default

Merge pull request adafruit#1502 from adafruit/tannewt-patch-7

Remove draft because is unpublishes releases

Merge pull request adafruit#1487 from tannewt/enable_displayio

Enable displayio on all Express boards.

Merge pull request adafruit#1404 from dhalbert/drivers.rst-typo

Prepare for 3.1.2 release: Link typo in drivers.rst; update frozen modules; fix nRF builds

Merge pull request adafruit#1394 from tannewt/fix_board_info

Fix build board info for python3.5

Merge pull request adafruit#1294 from tannewt/stack_check

Add stack validity check and raise an error when it happens.

Merge pull request adafruit#1339 from dhalbert/3.x-frozen-swap

Merge 3.x .frozen and /lib swap on sys.path; update frozen libs