Adding initial Teensy 3 support, compiles, but not fully functional yet.

- CDC Output seems to be working
- USB Keyboard output has not been tested, but is "ready"
- UART and Timers have not been tested, or fully utilized
- Issues using Timer 0
- Initial template for MBC-55X Scan module (only module currently compatible with the arm build)
- Updated the interface to the AVR usb module for symmetry with the ARM usb module
- Much gutting was done to the Teensy 3 usb keyboard module, though not in an ideal state yet

USB/pjrc/arm/usb_serial.h

@@ -0,0 +1,25 @@
+#ifndef USBserial_h_
+#define USBserial_h_
+
+#include <inttypes.h>
+
+// Compatibility defines from AVR
+#define PROGMEM
+#define PGM_P  const char *
+#define PSTR(str) (str)
+
+
+int usb_serial_getchar(void);
+int usb_serial_peekchar(void);
+int usb_serial_available(void);
+void usb_serial_flush_input(void);
+int usb_serial_putchar(uint8_t c);
+int usb_serial_write(const void *buffer, uint32_t size);
+void usb_serial_flush_output(void);
+extern uint8_t usb_cdc_line_coding[7];
+extern volatile uint8_t usb_cdc_line_rtsdtr;
+extern volatile uint8_t usb_cdc_transmit_flush_timer;
+extern volatile uint8_t usb_configuration;
+
+#endif // USBserial_h_
+