Fastest IO toggle

Hey, thanks for the post - that looks good! I can't think of any other obvious ways to make it significantly faster. At some point it'd be nice to have a 'fast path' for GPIO in compiled code, but it's not really that high up the priority list.

I guess the other (slightly cheaty) options are:

• Use the inline assembler and access the registers for B2 directly. I imagine that could hit in the region of 10Mhz.
  
• Use SPI and send the bit pattern 01010101.
  
• Use PWM via analogWrite