Ergodox Infinity: Add EE_HANDS support.

[firetech]

Add EE_HANDS support to Ergodox Infinity.

Description

Ergodox Infinity doesn't use the split_common framework, but either half (or both) can be connected to the computer (with the second half optionally connected to that half, to make them behave as a single keyboard). Currently, the two halves must be flashed with separate firmwares to be able to work "in both directions", which requires QMK to be rebuilt with MASTER=right.

This PR adds the ability to use the EE_HANDS feature on Ergodox Infinity, making it possible to flash both halves with the same firmware and still have them behave properly, regardless of how the two halves are connected to the computer. I also added a guide to set the required EEPROM values (in ergodox_infinity/readme.md), as it's currently a bit awkward on devices using dfu-util.

Types of Changes

• Core
• Bugfix
• New feature
• Enhancement/optimization
• Keyboard (addition or update)
• Keymap/layout/userspace (addition or update)
• Documentation

Checklist

• My code follows the code style of this project.
• My change requires a change to the documentation.
• I have updated the documentation accordingly.
• I have read the CONTRIBUTING document.
• I have added tests to cover my changes.
• I have tested the changes and verified that they work and don't break anything (as well as I can manage).

[firetech]

Quite sure the Travis errors are unrelated...

[drashna]

Travis CI errors are community layouts not designed for the ergodox infinity. So should be fine.

[stale]

Thank you for your contribution!
This pull request has been automatically marked as stale because it has not had activity in the last 45 days. It will be closed in 30 days if no further activity occurs. Please feel free to give a status update now, or re-open when it's ready.
For maintainers: Please label with awaiting review, breaking_change, in progress, or on hold to prevent the issue from being re-flagged.

[noroadsleft]

__attribute__ ((weak)) ✔️

[fauxpark]

#pragma weak

[stale]

Thank you for your contribution!
This pull request has been automatically marked as stale because it has not had activity in the last 45 days. It will be closed in 30 days if no further activity occurs. Please feel free to give a status update now, or re-open when it's ready.
For maintainers: Please label with awaiting review, breaking_change, in progress, or on hold to prevent the issue from being re-flagged.

[zvecr]

Thanks!