I2C @ PB6/PB7
Scan available addresses, read/write data directly or over DMA

Proto:

i0..2 - setup I2C with lowest..highest speed (7.7, 10 and 100kHz)
Ia addr - set I2C address
Ig - dump content of I2Cbuf
Iw bytes - send bytes (hex/dec/oct/bin) to I2C
IW bytes - the same over DMA
Ir reg n - read n bytes from I2C reg
I2 reg16 n - read n bytes from 16-bit register
In n - just read n bytes
IN n - the same but with DMA
Is - scan I2C bus
U - send long buffer over USART
