Heads up: fixed work coordinate setting with G10; might need changes in your coordinate system GCode

[Henner Zeller]

Hi,
Setting a work coordinate system was not entirely standard conformant
in BeagleG: The coordinates given in G10 were relative to the bottom
left corner of the machine cube.

However, these coordinates are supposed to be relative to the _machine
origin_, which is essentially where the home switches are. This has
now been fixed in BeagleG to be standard conformant.
So this means that e.g. if the Z-axis is homed at the top, all valid Z
coordinates are actually negative.

If you have not set-up a G54 coordinate system, your (0,0,0) position
is now where the machine origin is (=home switches), not at the
left-front-bottom position of the machine cube.

If you have the home switches at the left-front-bottom corner of your
machine (i.e. all home-pos=min in your configuration file), nothing
changes for you.

Otherwise, for all home-switches at a max position, only negative
coordinates are valid relative from this zero (as positive coordinates
would go beyond max).
Typically, you want to set up the most convenient default coordinate
system for you and store its position in the parameter file; I've
written a little paragraph that helps illustrate that:

https://github.com/hzeller/beagleg/blob/master/G-code.md#coordinate-systems

There are also some smaller other changes
- Even if no persistent parameter file is given (using the --param
flag), the default coordinate system
is G54. If the param file is given, the last used coordinate
system is activated.
- Doing G10 in relative mode (G91) updates the coordinate system
relative to its old position.
- The current active coordinate system is printed _after_ the
coordinates as response to the M114
command.

-h