Smartrap improvements

Version 2 - 7/1/2014
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- set screw version of herringbone pinion
- Servoless auto-level for Z-axis - J-head version
Version 3 - 7/5/2014
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**X-end improvements**
- I added a mount for a 40x40mm bed fan behind the hot-end mount. There is just enough room for this fan so that it does not hit the bed, the endstop, or the X-axis motor. Use 2x M3x25mm screws and nuts.
- I opened the mounting holes for the Z-endstop switch mounting plate. Now it is easier to get the M3 nuts in and connected to the screws.
- I tightened the Z-endstop switch mounting plate so that it holds a standard microswitch a little tighter. If the microswitch still wobbles in the mounting plate, use some hot glue from a glue gun to hold it in place.