Commit history, logo license, full-arc fix.

- Commit history added to repo, as an easier way for people to see view
the changes over time.

- Grbl logo copyright license added. All rights reserved with regards
to the Grbl logo.

- G2/3 full circles would sometime not execute. The problem was due to
numerical round-off of a trig calculation. Added a machine epsilon
define to help detect and correct for this problem. Tested and should
not effect general operation of arcs.

grbl/motion_control.c

@@ -100,9 +100,9 @@
   // CCW angle between position and target from circle center. Only one atan2() trig computation required.
   float angular_travel = atan2(r_axis0*rt_axis1-r_axis1*rt_axis0, r_axis0*rt_axis0+r_axis1*rt_axis1);
   if (is_clockwise_arc) { // Correct atan2 output per direction
-    if (angular_travel >= 0) { angular_travel -= 2*M_PI; }
+    if (angular_travel >= -ARC_ANGULAR_TRAVEL_EPSILON) { angular_travel -= 2*M_PI; }
   } else {
-    if (angular_travel <= 0) { angular_travel += 2*M_PI; }
+    if (angular_travel <= ARC_ANGULAR_TRAVEL_EPSILON) { angular_travel += 2*M_PI; }
   }
 
   // NOTE: Segment end points are on the arc, which can lead to the arc diameter being smaller by up to