Minor project update

Project archive Version 200621 with some helpful comments to steer students away from main() testing problems before reaching the lecture that deals with this special case.

Course content fixes & tools update

• Docker image requires updated base image that was missing make and gcc
• Ceedling updated to 0.30.0
• The diy mini-project is now future proofed with its own local copy of Unity
• Updated awesomesauce2 project archive

Go live course content

• Added Docker image documentation
• course script now includes guard warning about files present in project expansion directory and offers optional deletion to clear expansion directory
• Latest course project archive (version 191217)

Environment & course content updates

• Top-level Docker image references base image that includes a Qemu patch to fix a runtime warning
• Latest course project with source and project file fixes

Image content updates in preparation for course going live

• Base image is now built on Ubuntu 18.04 (in part for latest certificate package support for Ruby & gems)
• Base image no longer strips out gcc-arm-none-eabi utilities
• Gems updated with Ceedling at version 0.29.1
• Latest course project content package