Open issues / next steps for libfaketime development

- add more functional tests that check more than the basic functionality
- use the testing framework to also implement unit tests
- make the new "limiting" and "spawning" features more flexible to use
  and available through the wrapper shell script
- fake timer_create and friends
- handle CLOCK_REALTIME_COARSE and CLOCK_MONOTONIC_COARSE
- work around thread local storage issue, e.g., by using pthreads