New startup script setting. New dry run, check gcode switches. New system state variable. Lots of reorganizing.

(All v0.8 features installed. Still likely buggy, but now thourough
testing will need to start to squash them all. As soon as we're done,
this will be pushed to master and v0.9 development will be started.
Please report ANY issues to us so we can get this rolled out ASAP.)

- User startup script! A user can now save one (up to 5 as compile-time
option) block of g-code in EEPROM memory. This will be run everytime
Grbl resets. Mainly to be used as a way to set your preferences, like
G21, G54, etc.

- New dry run and check g-code switches. Dry run moves ALL motions at
rapids rate ignoring spindle, coolant, and dwell commands. For rapid
physical proofing of your code. The check g-code switch ignores all
motion and provides the user a way to check if there are any errors in
their program that Grbl may not like.

- Program restart! (sort of). Program restart is typically an advanced
feature that allows users to restart a program mid-stream. The check
g-code switch can perform this feature by enabling the switch at the
start of the program, and disabling it at the desired point with some
minimal changes.

- New system state variable. This state variable tracks all of the
different state processes that Grbl performs, i.e. cycle start, feed
hold, homing, etc. This is mainly for making managing of these task
easier and more clear.

- Position lost state variable. Only when homing is enabled, Grbl will
refuse to move until homing is completed and position is known. This is
mainly for safety. Otherwise, it will let users fend for themselves.

- Moved the default settings defines into config.h. The plan is to
eventually create a set of config.h's for particular as-built machines
to help users from doing it themselves.

- Moved around misc defines into .h files. And lots of other little
things.

gcode.c

@@ -177,7 +177,7 @@ uint8_t gc_execute_line(char *line)
         switch(int_value) {
           case 0: gc.program_flow = PROGRAM_FLOW_PAUSED; break; // Program pause
           case 1: // Program pause with optional stop on, otherwise do nothing.
-            if (bit_istrue(sys.switches,BITFLAG_OPT_STOP)) {
+            if (bit_istrue(gc.switches,BITFLAG_OPT_STOP)) {
               gc.program_flow = PROGRAM_FLOW_PAUSED; 
             }
             break; 
@@ -253,13 +253,20 @@ uint8_t gc_execute_line(char *line)
      NOTE: Independent non-motion/settings parameters are set out of this order for code efficiency 
      and simplicity purposes, but this should not affect proper g-code execution. */
   
+  // ([F]: Set feed rate. Already performed, but enforce rapids for dry runs.)
+  if (bit_istrue(gc.switches,BITFLAG_DRY_RUN)) { gc.feed_rate = settings.default_seek_rate; }
+  
   //  ([M6]: Tool change should be executed here.)
   
   // [M3,M4,M5]: Update spindle state
-  spindle_run(gc.spindle_direction); //, gc.spindle_speed);
+  if (!(gc.switches & (BITFLAG_DRY_RUN | BITFLAG_CHECK_GCODE))) {
+    spindle_run(gc.spindle_direction); //, gc.spindle_speed);
+  }
   
   // [*M7,M8,M9]: Update coolant state
-  coolant_run(gc.coolant_mode);
+  if (!(gc.switches & (BITFLAG_DRY_RUN | BITFLAG_CHECK_GCODE))) {
+    coolant_run(gc.coolant_mode);
+  }
   
   // [G54,G55,...,G59]: Coordinate system selection
   if ( bit_istrue(modal_group_words,bit(MODAL_GROUP_12)) ) { // Check if called in block
@@ -275,8 +282,11 @@ uint8_t gc_execute_line(char *line)
     case NON_MODAL_DWELL:
       if (p < 0) { // Time cannot be negative.
         FAIL(STATUS_INVALID_STATEMENT); 
-      } else { 
-        mc_dwell(p); 
+      } else {
+        // Ignore dwell in dry run and check gcode modes
+        if (!(gc.switches & (BITFLAG_DRY_RUN | BITFLAG_CHECK_GCODE))) {
+          mc_dwell(p); 
+        }
       }
       break;
     case NON_MODAL_SET_COORDINATE_DATA:
@@ -537,7 +547,7 @@ uint8_t gc_execute_line(char *line)
   
   // M0,M1,M2,M30: Perform non-running program flow actions. During a program pause, the buffer may 
   // refill and can only be resumed by the cycle start run-time command.
-  if (gc.program_flow || bit_istrue(sys.switches,BITFLAG_SINGLE_BLOCK)) {
+  if (gc.program_flow || bit_istrue(gc.switches,BITFLAG_SINGLE_BLOCK)) {
     plan_synchronize(); // Finish all remaining buffered motions. Program paused when complete.
     sys.auto_start = false; // Disable auto cycle start. Forces pause until cycle start issued.