Changed safety door/parking handling to be compliant with legacy Grbl.

Added $384 setting for controlling G92 offset persistence.
Improved $help command output and handling.
Moved the optional tool table in non-volatile storage.
Added gcode parameter support and optional expression support.

CMakeLists.txt

@@ -23,6 +23,9 @@ target_sources(grbl INTERFACE
  ${CMAKE_CURRENT_LIST_DIR}/tool_change.c
  ${CMAKE_CURRENT_LIST_DIR}/alarms.c
  ${CMAKE_CURRENT_LIST_DIR}/errors.c
+ ${CMAKE_CURRENT_LIST_DIR}/ngc_params.c
+ ${CMAKE_CURRENT_LIST_DIR}/ngc_expr.c
+ ${CMAKE_CURRENT_LIST_DIR}/regex.c
 )
 
 target_include_directories(grbl INTERFACE ${CMAKE_CURRENT_LIST_DIR})