2.2.6 - Wire.h fix on several levels

In 2.2.4, I tried to pull in a change for a problem with I2C baud rate calculation. But I actually made things much worse because I only pulled in half of it. This gets the other half. It also adds hardening against the widespread and long-standing TWI errata, by having it ensure that it's pins are set appropriately when Wire.begin() is called. a method to enable pullups with Wire.usePullups(). It also adds a bit more documentation for the wire library Also, the SPI library no longer requires the SS pin to be specified, since there is literally nothing special about it the way the SPI library sets it up SPI.h is master only (SPI.h got major work done on DxCore - I didn't bother bringing the Dx-specific stuff back here, but I did remove SS pin requirement.