Final minor updates for master release.

- Updated ShapeOko2 defaults based on machine testing of the basic
model provided by Inventables. (or close to it.) Should be pretty
conservative but much faster than before. For example, X and Y axes are
set at (10x) faster at 5000mm/min. It can run much faster than this,
but this seems like a safe speed for everyone.

- Updated README for master release.

- Added some new settings methods for clearing the EEPROM when changing
versions. Needs some more work, but it should ok for master release.
Should work on it more for the next version.