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.

doc/log/commit_log_v1.1.txt

@@ -1,3 +1,32 @@
+----------------
+Date: 2016-10-27
+Author: Sonny Jeon
+Subject: Spindle speed overrides behavior tweak. New experimental laser dynamic power mode.
+
+- Spindle speed overrides now update immediately if they are changed
+while in a HOLD state. Previously, they would update after exiting the
+HOLD, which isn’t correct.
+
+- New experimental dynamic laser power mode that adjusts laser power
+based on current machine speed. Enabled by uncommenting
+LASER_CONSTANT_POWER_PER_RATE in config.h
+
+  - It assumes the programmed rate is the intended power/rate for the
+motion.
+  - Feed rate overrides (FRO) do not effect the power/rate. Meaning
+that spindle PWM will automatically lower with lower FRO and increase
+with higher FRO to keep it the same.
+  - Spindle speed overrides (SSO) will directly increase and decrease
+the power/rate. So 150% SSO will increase the PWM output by 150% for
+the same speed.
+  - The combination of FRO and SSO behaviors should allow for subtle
+and highly flexible tuning of how the laser cutter is operating in
+real-time and during the job.
+
+- Re-factored planner block rapid rate handling for the dynamic laser
+power feature. Should have had no effect on how Grbl operates.
+
+
 ----------------
 Date: 2016-10-26
 Author: Sonny Jeon