0.2

CHANGES:

• trace-tef: additional argument to with_setup; env for "stdout"/"stderr"
• refactor: avoid conflicting with stdlib Trace module by adding sublibrary trace.core.
  Programs that use compiler-libs.toplevel should use trace.core
  directly, because using trace will cause linking errors.
• perf(trace-tef): improve behavior of collector under contention by
  pulling all events at once in the worker