Fixed Wire library init on nRF52 targets
The Cortex-M3/4 in nRF52 devices is capable of having hardware I2C on any of its SERCOM devices, Arduino's library support (and Adafruit) chose to use a single SERCOM for I2C. Therefore, the Wire.begin(SDA, SCL) option is not implemented. In the previous version of BitBang_I2C, I had excluded only AVR targets for lacking this feature, but now I've had to add nRF52 to that list.