- Explicitly say in cmpxchg that "weak" is boolean.
- The signature of the trap handler and the new_thread API are corrected
  so that input parameters are values and output parameters are pointers
  to values.
- In trap handler, the "values" array is now a pointer to a
  client-allocated array. The client is also responsible for freeing it
  by providing a "freer". This is solely for working around the C
  programming language's limitation that "raw arrays (T*) do not know
  how to deallocate themselves". Garbage-collected languages (such as
  Haskell, Java, ...) and ownership-based languages (C++, rust) do not
  have such problems.