GPX 2.2.1 -- another unofficial release

These are unofficial GPX 2.2.1 releases which incorporate some fixes as well as some changes. See the commit history for what these all entail.

This release incorporates Mark Walker's changes to support Octoprint, https://github.com/markwal/OctoPrint-GPX. This release also allows digipot settings to range from 0 to 255, inclusive. Prior releases of GPX limited the values to the range 0 to 127 which is sufficient for MightyBoard electronics. However, the Azteeg X3 uses ranges as high as 255. Moreover, the firmwares have always self-limited the X3G values to the range appropriate to the underlying hardware.

GPX 2.1 alpha -- an unofficial GPX release

These are unofficial GPX 2.1 alpha releases which incorporate some fixes as well as some changes. See the commit history for what these all entail.

The builds for Windows do NOT include USB / serial IO support. That because making a single executable with no DLL dependencies is more time than I care to invest. GPX can be built with USB / serial IO support on Windows with Cygwin, but that then requires providing a number of DLLs with the executable. I've built these Windows executables with MinGW but without USB / serial IO support. (Lack of POSIX termios support being the issue.)