luigetter: coding style

Signed-off-by: Jeff Epler <jepler@unpythonic.net>
luigetter: doc fixes

Signed-off-by: Jeff Epler <jepler@unpythonic.net>
luigetter: additional getters

Signed-off-by: Jeff Epler <jepler@unpythonic.net>
lui-test: test gcode / mcode getters

Signed-off-by: Jeff Epler <jepler@unpythonic.net>