2.0.0

BREAKING CHANGE: removed the second standard_deviation argument.
mimir now takes NUMBER[SUFFIX]... (s/m/h/d, summed like sleep) or inf, plus --help/--version — matching coreutils' sleep instead of a bespoke interface.

Also:

• resolve esleep*.wav relative to the script (or $MIMIR_AUDIO_DIR)
  instead of hardcoding /usr/local/share/mimir
• drop the bc dependency, do all float math in awk
• seed the Gaussian speed/delay draws from $RANDOM instead of
  spawning od per sample
• handle SIGTERM in addition to SIGINT; tolerate sox failures
  without aborting the sleep
• add shell.nix for a reproducible dev/test environment
• update README for the new CLI and dependencies