Conflicts with AVR `util/atomic.h`

[matthijskooijman]

Conflicts with AVR `util/atomic.h`

[wizard97]

If, in a single sketch, both util/atomic.h and SimplyAtomic.h are included, compilation fails:

Yeah, I noticed this on my own a while ago and never got around to fixing it. I just did as you suggested and prefixed all custom methods and macros with SA_

On an unrelated note, I see that this code is based on AVR's
util/atomic.h, but the license notice is not preserved, which violates
the license of that code. One could argue that this code is too simple
to apply copyright to, but just keeping the license wouldn't hurt. Now,
there is no license attached at all, which would prevent people from
redistributing (binaries containing) this code.

Fixed this as well! Thanks for pointing it out. I put the entire project under a BSD license as well in order to be compatible with the AVR's methods I pulled from util/atomic.h.