Remove unnecessary register read for triggered measurement & new function getConversionReady

Removed unnecessary comment.

Note: ConversionReady only gets reset if getBusPower is called (or the Configuration Register is written somehow)!

Note: ConversionReady only gets reset if getBusPower is called (or the Configuration Register is written somehow)!

According to the datasheet reading the INA219_BUS_REG does not clear the CNVR flag. Reading the INA219_PWR_REG instead would clear the CNVR flag.
Since the INA219_CONF_REG is written afterwards anyways, even a read of the INA219_PWR_REG would be unnecessary.
Checked the behaviour with the Triggerd example and everything seems to be fine.
Thank you for your efforts!

Avoid infinite loop while waiting for conversion in startSingleMeasurement

Added timeout option for single measurement.