Add alternate address to begin()

[jbaumann]

This patch adds an additional optional parameter to the begin() method, the i2c_address. This allows to switch from the default address of the sensor to the alternate address. Fixes issue "Add alternative I2C address as parameter for the begin() method #7"

[ladyada]

thanx ! how do you get the alternative address on the hardware?

[ladyada]

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[bukwyrm]

This is ready to be merged, mayhaps? - The 39 adress is the 'default-alternative' and can be produced by pulling ADR to Vcc

[caternuson]

Is there a different variant out there? Where is the ADR pin?

[jbaumann]

The AHT10 has an additional ADR pin that is exposed on many boards.

[caternuson]

Ah, OK. It's for the AHT10:

[caternuson]

@ladyada LGTM. The CP lib allows for this as well. I suggest we allow this to be a breaking change so the parameters can be in this order for the sake of consistency :

  bool begin(uint8_t i2c_address = AHTX0_I2CADDR_DEFAULT, TwoWire *wire = &Wire , int32_t sensor_id = 0);