First SPIN version of update() and lookup(), with a test() process
Add README
Add web link to SPIN in README
Bug fix. Add collect() function

* Use d_step instead of atomic for cmpXchg(), it should be more efficient.

* Implement min().

* Fix bug in advance(), we forgot to exit the loop.

* Implement collect().
In update(), stop the process if we reach end of log
Prove the program is memory-safe, i.e. no thread accesses log entries below gc
Threads now call collect(). Memory-safety is still proved