TWI_MasterSetBaud hides functionality

According to the TWI sections of the documentation [here](https://content.arduino.cc/assets/Nano-Every_processor-48-pin-Data-Sheet-megaAVR-0-series-DS40002016B.pdf) and [here](http://ww1.microchip.com/downloads/en/DeviceDoc/megaAVR0-series-Family-Data-Sheet-DS40002015B.pdf) the TWI baud rate is variable through the whole range of 0Hz - 1 MHz. The implementation of the Wire library for the megaavr however explicitly hides that functionality in a hidden way.

I suggest removing the code that limits the baudrate to the 3 distinct values defined in the Philips I2C standard in order to be able to communicate with devices that do not match that standard.

Locate TWI_MasterSetBaud in the megaavr Wire library and compare its current baud-rate restriction with the linked megaAVR TWI documentation. Verify how baud values are selected, then consider the work complete when the documented 0 Hz–1 MHz range is available instead of only the three Philips I2C standard values.

Written by the indexing model from the issue text.