Added USART SPI for 32u4 Leonardo/Micro

[NicoHood]

USART SPI gives us the option to use the SPI for other interfaces and still update leds even faster than with bitbang SPI.

A board that optionally breaks out the TX Led pin is required. For example there are some 32u4 breakout boards and the Pololu Mini board which also breaks out all pins.

Note that you should change the TX Led to another pin.
This can be done by editing the variants file. You may use Led 13 as TX indicator Led instead.

Patch for the variants file in Arduino/hardware/arduino/avr/variants/leonardo/pins_arduino.h

#define TX_RX_LED_INIT  DDRC |= (1<<7), DDRB |= (1<<0)
#define TXLED0          PORTC &= ~(1<<7)
#define TXLED1          PORTC |= (1<<7)
#define RXLED0          PORTB |= (1<<0)
#define RXLED1          PORTB &= ~(1<<0)

A more fancy patch can also be created with a custom hardware folder which contains a duplicated, patched pins_arduino.h file.

Add new leds like this:

FastLED.addLeds<CHIPSET,SPI_UART1_DATA, SPI_UART1_CLOCK, COLOR_ORDER>(leds, NUM_LEDS).setCorrection(CORRECTION);

Since pin 24 wont't work for attaching anyways we can still enable Hardware USART SPI for those users who understand what they are doing (or pretend to) without patching FastLED on every update.

All code was tested with a Pololu Mini LV board, the patches above and 25 WS2801 leds. Got an FPS gain of 100%.