Further planner improvements and misc minor bug fixes. Memory savings and increased buffer size.

- Update grbl version and settings version to automatically reset
eeprom. FYI, this will reset your grbl settings. - Saved
3*BLOCK_BUFFER_SIZE doubles in static memory by removing obsolete
variables: speed_x, speed_y, and speed_z. - Increased buffer size
conservatively to 18 from 16. (Probably can do 20). - Removed expensive!
modulo operator from block indexing function. Reduces significant
computational overhead. - Re-organized some sqrt() calls to be more
efficient during time critical planning cases, rather than non-time
critical. - Minor bug fix in planner max junction velocity logic. -
Simplified arc logic and removed need to multiply for CW or CCW
direction.

script/grbl_preprocess.py

@@ -8,6 +8,8 @@ G-code preprocessor for grbl (BETA!)
 - OPTIONAL: Remove unsupported grbl G and M commands
 
 TODO: 
+- Number precision truncation
+- Arc conversion option
 - More robust error checking
 - Improve interface to command line options
 - Improve g-code parsing to NIST standards