Added build pipeline (#1)

[anabolyc]

Hey

I decided to follow your steps and after spending some time and resolving small issues here and there decided to document my progress via code and build pipeline
This changeset does following

• Adds submodules for every dependency, this allows better dependency tracking and more stable builds
• Adds build pipeline, all steps are run via Github Action on push and produce all artifacts that you'd need to flash your device
• Adds release pipeline, so tagged commit will automatically produce release with all artifacts included, like this one
• Updated manual build scripts to take above changes into account. They should still work

I'm planning to work on this further. This looks fantastically interesting and useless, just kind of stuff hobbyists would like to do. I'm thinking to re-create it in custom hardware, let me kno if you're interested to collab on this.