Enable platformio support.

[positron96]

This PR adds a simple platform.io file that builds a file for Arduino Uno. Its output exactly matches what Arduino IDE creates.

Having platformio file in this repo allows developers to use "normal" IDEs with autocomplete, refactoring and stuff, while maintaining Arduino compatibility. It also will allow easy autobuilding of release builds with CI/CD pipelines (with pio CLI).

Full compatibility with Arduino IDE is retained (it still works)

[ooxi]

While not opposed to the PR, I don't really see a benefit, since a Makefile is already present? Moreover, those commits should be squashed before creating a PR.

[positron96]

I'll squash the commits in the nearest future.
Anyway, could you elaborate more on Makefiles? It makes no difference for PIO users since PlatformIO uses its own build system (in a way, PIO is a build system)

[avion23]

This MR would help me tremendously.

I can see that there is already a make-system. But platformio is the one build system to rule them all and supports all kinds of flashers and bootloaders.

[dsiguero]

What's the rationale for not merging this?

[rob-deutsch]

I would also like to see this merged. PlatformIO is a wonderful build system which makes it much easier to get up and running with GRBL.

[NuwanJ]

Agree with you @rob-deutsch. Having a Makefile is ok. But platformio.ini is more than a build config file, which allows to compile/build GRBL with VS Code + Platform IO easily.

[mydani]

One more voting for the merge of this PR - platformio is status-quo for sophisticated development.