silence warnings properly
don't cast away constness if at all possible
compile to ram
usart guard time/prescaler
use standard attributes instead of __attribute__

yes, i know this will break the code for anything that does not
know the attributes i'm using, instead of failing to parse outright. but
then again, people that compile without warnings are kind of strange
anyway.
proper operators for gpio
special-case *_mask for bitarrays