Updates on Mar 12. 2020.

'ota' module updated
  - update can be performed via 'requests.get'
  - some bug fixes and improveents

'ulab' module updated to latest GitHub master

MicroPython core updated
  - backported some code needed to run latest 'ulab
  - objexcept.c, sequence.c, obkstrunicode.c,
    objslice.c, runtime.h, runtime.c, obj.h

'machine' module updated

'spi' module updated
  - many changes to SPI slave

updated littlefs 'trim' function

'network' module updated
  - TLS/SSL is now available for GSM connections
  - secure connection in sockets, requests and mqtt now works over GSM connection

'requests' module updated
  - support for OTA update added
  - resume download is now implemented

fixed bug in 'uart' module

bug fixes in mbedtls (FreeRTOS)

other bugfixes and improvements