PyPi documentation fix

PyPi documentation fix.

Added is_conversion_ready() function to check if a new reading is available

The is_conversion_ready() function checks if the INA219 has updated the registers with a new reading, this can be used to guarantee that a measurement represents a new reading, not the previous reading. The method is checking bit CNVR in the voltage register according to INA219 datasheet.

Update to use named logger rather than the root logger

Allows a main module module to configure root logger using basicConfig() if required.

Support addressing i2c bus numbers > 1

A new parameter 'busnum' has been added to the INA219 class contructor this is the I2C bus number for the device platform, defaults to auto detects 0 or 1 for Raspberry Pi or Beaglebone Black (optional).