I2C errors handling

[begreeen]

Implement error handling for both situations:

• ACK errors in I2C high-level implementation in I2C.h
• add timeout in while loop in SoftI2C.h implementation; add error return.

Probably one error state is sufficient?

[ggajoch]

Just found that reading 0 bytes hangs up the I2C completely. This seems to be not supported in TWI module. Check should be added.