Allow LTC2451 I2C command retry while conversion in progress

The LTC2451 ADC does not respond to I2C commands while a conversion in progress. This can cause problems if subsequent reads are performed too close together.

This addresses the issue by allowing each I2C command to fail (catch ComIOException) once. The class then waits for ~45ms (longest conversion time) and retries the command. If the command fails the second time, then the exception is forwarded.