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.

README.md

@@ -40,6 +40,8 @@ Grbl includes full acceleration management with look ahead. That means the contr
 
 - **Laser Mode** : The new "laser" mode will cause Grbl to move continuously through consecutive G1, G2, and G3 commands with spindle speed changes. When "laser" mode is disabled, Grbl will instead come to a stop to ensure a spindle comes up to speed properly. Spindle speed overrides also work with laser mode so you can tweak the laser power, if you need to during the job. Switch between "laser" mode and "normal" mode via a `$` setting.
 
+	- **Dynamic Laser Power Scaling with Speed** : (Optional) If your machine has low accelerations, this option will automagically scale the laser power based on how fast Grbl is traveling, so you won't have burnt corners when your CNC has to make a turn! Currently available as a compile-time option until vetting is complete. Operation may be tweaked in future versions. 
+
 - **Sleep Mode** : Grbl may now be put to "sleep" via a `$SLP` command. This will disable everything, including the stepper drivers. Nice to have when you are leaving your machine unattended and want to power down everything automatically. Only a reset exits the sleep state.
 
 - **Significant Interface Improvements**: Tweaked to increase overall performance, include lots more real-time data, and to simplify maintaining and writing GUIs. Based on direct feedback from multiple GUI developers and bench performance testing. _NOTE: GUIs need to specifically update their code to be compatible with v1.1 and later._