Names with two leading underscores are reserved in any context of the c
standard, and thus must not be used. This ATmega platform used it however for
defining internal stuff. This commit fixes this.
The brr calculation on the datasheet is different than what is implmented.
This is intentional since it provides better rounding due to truncation.
There was no comment explaining that so this comment should prevent confusion.
* Add support for U2X switch to double transmission speed
* Provides lower error rates when needed
* Add support for static baud rate calculation, reduces computation by 10x
* adds support for statically enabling double speed baud
