omnia-mcutool: Bump to 0.3-rc3

• The --upgrade option will now work even if MCU is in bootloader (for example if previous upgrade was aborted).

• On boards with GD32 MCUs, omnia-mcutool will now refuse to upgrade application firmware to version lower than 4.1 if bootloader version is 2.0 (the original for first batch of boards with GD32 MCUs) since these versions of application and bootloader are not compatible.

  If user already upgraded to such a combination, an upgrade of bootloader firmware is required.

  The --upgrade option will inform about this and will automatically upgrade bootloader firmware if the --force option is given.

  (Note that version 4.1 of the MCU firmware was will be released soon, once it is properly tested.)

• Various other improvements.