Improved constant laser power per rate mode. Re-factored for flash size. Minor bug fixes.

- NOTE: This commit has largely been untested.

- Constant laser power per rate mode has been improved. Altered its
implementation to be more responsive and accurate.

- Based on LaserWeb dev feedback, only G1, G2, and G3 moves operate
with constant laser power mode. Meaning that G0, G38.x, and $J jogging
motions operate without it and will keep a constant power output. This
was specifically requested as a way to focus the laser by keeping the
laser on when not moving. Operationally, this shouldn’t alter how the
laser mode operates.

- Re-factored parts of the g-code parser and g-code state reports to
save a few hundred bytes of flash. What was done makes the code a bit
more unreadable (bad), but the flash space was in dire need. So, I’m
willing to live with it for now.

- Fixed a problem with $G g-code state reports. Showed `M0` program
pause during a run state. Now fixed to show nothing during a run state.
Also, `M30` program end was shown as `M2`. This was also corrected.

- Improved spindle stop override responsiveness by removing the
enforced spindle restoring delay. It’s not needed for a feature that is
user controlled.

- Fixed a bug with G2/3 arcs in inverse time mode.

- Updated the interface.md document to make it more clear how WPos: or
MPos: can be calculated from WCO:. Some GUI devs have failed to catch
this in the documentation.

grbl/planner.h

@@ -40,7 +40,7 @@
 #define PL_COND_FLAG_RAPID_MOTION      bit(0)
 #define PL_COND_FLAG_SYSTEM_MOTION     bit(1) // Single motion. Circumvents planner state. Used by home/park.
 #define PL_COND_FLAG_NO_FEED_OVERRIDE  bit(2) // Motion does not honor feed override.
-#define PL_COND_FLAG_INVERSE_TIME      bit(3)
+#define PL_COND_FLAG_INVERSE_TIME      bit(3) // Interprets feed rate value as inverse time when set.
 #define PL_COND_FLAG_SPINDLE_CW        bit(4)
 #define PL_COND_FLAG_SPINDLE_CCW       bit(5)
 #define PL_COND_FLAG_COOLANT_FLOOD     bit(6)