Light-weight, asynchronous logging built around `clojure.core/tap>`.

Follows the same pattern as `clojure.core/assert`: When tracing is not compiled,
the tracing macros should create no runtime overhead.

When tracing is compiled, a check occurs to see if tracing is enabled; only then
do the most expensive operations (e.g., identifying the function containing the
trace call) occur, as well as the call to `clojure.core/tap>`.