Cleaned-up limit pin reporting and comments.

- Cleaned up the limit pin state reporting option to display only the
state per axis, rather than the whole port. It’s organized by an XYZ
order, 0(low)-1(high), and generally looks like `Lim:001`.

- Separated the control pin state reporting from limit state reporting
as a new compile option. This stayed the same in terms of showing the
entire port in binary, since it’s not anticipated that this will be
used much, if at all.

- Updated some of the gcode source comments regarding supported g-codes.

grbl/gcode.c

@@ -1056,9 +1056,9 @@ uint8_t gc_execute_line(char *line)
    group 1 = {G81 - G89} (Motion modes: Canned cycles)
    group 4 = {M1} (Optional stop, ignored)
    group 6 = {M6} (Tool change)
-   group 7 = {G40, G41, G42} cutter radius compensation
-   group 8 = {G43} tool length offset (But G43.1/G94 IS SUPPORTED)
-   group 8 = {*M7} enable mist coolant
+   group 7 = {G41, G42} cutter radius compensation (G40 is supported)
+   group 8 = {G43} tool length offset (G43.1/G49 are supported)
+   group 8 = {*M7} enable mist coolant (* Compile-option)
    group 9 = {M48, M49} enable/disable feed and speed override switches
    group 10 = {G98, G99} return mode canned cycles
    group 13 = {G61, G61.1, G64} path control mode