Implementing new 8/16bit i2c API.

New functions and their Lua interfaces:
platform_i2c_read8()	i2c.read8()
platform_i2c_write8()	i2c.write8()
platform_i2c_read16()	i2c.read16()
platform_i2c_write16()	i2c.write16()

All these new functions handle START/STOP conditions internally
and knows how to send devices internall address to the bus.
Some devices use internally 8bit registerr offset while others
use 16bit internal offsets.