Build options for Keyboard:
NKRO_ENABLE - NKRO shares interface 0 with Boot/6KRO
this can save Endpoint resources of MCU
NKRO_6KRO_ENABLE - NKRO has its own interface
this is equivalent to old NKRO impl.
Otherwise - Boot/6KRO interface 0 only
Modified the LUFA USB HID Descriptor to change the logical/usage
minimums for System Control from 0x01 (Mouse) to 0x81 (System Power
Down), this fixes OS X recognizing the Planck as having a mouse and
tablet, even with mousekeys off.