Added I2C_Muxer object.... an I2C Mutiplexer board to connect mutible devices with the same address to a single I2C bus.
Every I2C bus can have 8 Muxers and every Muxer has 8 Sub busses.

Fixed I2C.scan() function, after the last 100KHz bugfix scan trew an IOError when no device whas on the scanned address.