Added block delete, opt stop, single block mode. New parser state and parameter feedback. Overhauled '$' command.

NOTE: Another incremental update. Likely buggy, still a ways to go
before everything is installed, such as startup blocks.

- Changed the '$' command to print help. '$$' now prints Grbl settings.
The help now instructs the user of runtime commands, switch toggling,
homing, etc. Jogging will be added to these in v0.9.

- Added switches: block delete, opt stop, and single block mode.

- Now can print the g-code parser state and persistent parameters
(coord sys) to view what Grbl has internally.

- Made the gc struct in the g-code parser global to be able to print
the states. Also moved coordinate system tracking from sys to gc struct.

- Changed up the welcome flag and updated version to v0.8c.

- Removed spindle speed from gcode parser. Not used.

config.h

@@ -149,7 +149,7 @@
 // TODO: The following options are set as compile-time options for now, until the next EEPROM 
 // settings version has solidified. This is to prevent having to support dozens of different
 // incremental settings versions.
-#define BLOCK_DELETE_ENABLE 0 // Block delete enable/disable flag during g-code parsing
+// -> NOW CODED INTO SETTINGS #define BLOCK_DELETE_ENABLE 0 // Block delete enable/disable flag during g-code parsing
 
 // This parameter sets the delay time before disabling the steppers after the final block of movement.
 // A short delay ensures the steppers come to a complete stop and the residual inertial force in the