Update nuts_bolts.c

Removed __floatunsisf and used normal casting on line 81. 
This makes it compatible with the Arduino IDE.
Update planner.c

Removed inline from all functions. 

If this is really needed is there another way that we can get 
around using it? (The Arduino IDE does not recognize it) 
Merge pull request #278 from EliteEng/master

Update Pin Change Interrupts on Mega 2560
Merge pull request #279 from EliteEng/master

Changed Stepper Pins
Add support for active-high limit switches
Merge pull request #289 from Travis-Snoozy/master

Add support for active-high limit switches
Pushed bug fixes. Updated readme.

- G18 plane select fix from XZ-plane to ZX-plane per right hand rule.

- Added volatile declaration for rx_buffer_tail in serial.c. No real
effect to operation as avr-gcc adds this upon compilation. Helps with
porting issues when using a different compiler.
added shapeoko2 profile

shapeoko 2 uses 2mm GT2 belting and 20tooth pulleys
Merge pull request #301 from shapeoko/master

added shapeoko2 profile
Update README.md
Merge pull request #201 from Protoneer/master

Made a few changes to make the code compatible with the Arduino IDE. Sorry about the tardiness!
Update README.md
Merge branch 'serial' of https://github.com/EliteEng/grbl into serial