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.

README.md

@@ -1,4 +1,4 @@
-![GitHub Logo](/doc/logo/Grbl Logo 250px.png)
+![GitHub Logo](/doc/media/Grbl Logo 250px.png)
 
 
 ***
@@ -27,8 +27,8 @@ Grbl includes full acceleration management with look ahead. That means the contr
 ***
 
 _**Master Branch:**_
-* [Grbl v0.9i Atmega328p 16mhz 115200baud with generic defaults](http://bit.ly/1EiviDk) _(2015-03-15)_
-* [Grbl v0.9i Atmega328p 16mhz 115200baud with ShapeOko2 defaults](http://bit.ly/1NYIfKl) _(2015-03-15)_
+* [Grbl v0.9i Atmega328p 16mhz 115200baud with generic defaults](http://bit.ly/1EiviDk) _(2015-03-29)_
+* [Grbl v0.9i Atmega328p 16mhz 115200baud with ShapeOko2 defaults](http://bit.ly/1NYIfKl) _(2015-03-29)_
   - **IMPORTANT INFO WHEN UPGRADING TO GRBL v0.9i:** 
   - Baudrate is now **115200** (Up from 9600). 
   - Variable spindle is now enabled by default. Z-limit(D12) and spindle enable(D11) have switched to access the hardware PWM on D11. Homing will not work if you do not re-wire your Z-limit switch to D12.