File re-organization. New Makefile.

- Re-organized source code files into a ‘grbl’ directory to lessen one
step in compiling Grbl through the Arduino IDE.

- Added an ‘examples’ directory with an upload .INO sketch to further
simplify compiling and uploading Grbl via the Arduino IDE.

- Updated the Makefile with regard to the source code no longer being
in the root directory. All files generated by compiling is placed in a
separate ‘build’ directory to keep things tidy. The makefile should
operate in the same way as it did before.

README.md

@@ -53,6 +53,8 @@ _**Archives:**_
   - **New Grbl SIMULATOR! (by @jgeisler and @ashelly):** A completely independent wrapper of the Grbl main source code that may be compiled as an executable on a computer. No Arduino required. Simply simulates the responses of Grbl as if it was on an Arduino. May be used for many things: checking out how Grbl works, pre-process moves for GUI graphics, debugging of new features, etc. Much left to do, but potentially very powerful, as the dummy AVR variables can be written to output anything you need. 
   - **Configurable Real-time Status Reporting:** Users can now customize the type of real-time data Grbl reports back when they issue a '?' status report. This includes data such as: machine position, work position, planner buffer usage, serial RX buffer usage.
   - **Updated Homing Routine:** Sets workspace volume in all negative space regardless of limit switch position. Common on pro CNCs. But, the behavior may be changed by a compile-time option though. Now tied directly into the main planner and stepper modules to reduce flash space and allow maximum speeds during seeking.
+  - **CoreXY Support:** Grbl now supports CoreXY kinematics on an introductory-level. Most functions have been verified to work, but there may be bugs here or there. Please report any problems you find!
+  - **Full Limit and Control Pin Configurability:** Limits and control pins operation can now be interpreted by Grbl however you'd like, with the internal pull-up resistors enabled or disabled, or reading a high or low as a trigger. This should cover all wiring and NO or NC switch scenarios.
   - **Optional Limit Pin Sharing:** Limit switches can be combined to share the same pins to free up precious I/O pins for other purposes. When combined, users must adjust the homing cycle mask in config.h to not home the axes on a shared pin at the same time. Don't worry; hard limits and the homing cycle still work just like they did before.
   - **Optional Variable Spindle Speed Output:** Available only as a compile-time option through the config.h file. Enables PWM output for 'S' g-code commands. Enabling this feature will swap the Z-limit D11 pin and spindle enable D12 pin to access the hardware PWM on pin D12. The Z-limit pin, now on D12, should work just as it did before.
   - **Additional Compile-Time Feature Options:** Line number tracking, real-time feed rate reporting.
@@ -68,6 +70,7 @@ List of Supported G-Codes in Grbl v0.9
   - Distance Modes: G90, G91
   - Plane Select Modes: G17, G18, G19
   - Tool Length Offset Modes: G43.1, G49
+  - Cutter Compensation Modes: G40
   - Coordinate System Modes: G54, G55, G56, G57, G58, G59
   - Program Flow: M0, M1, M2, M30*
   - Coolant Control: M7*, M8, M9