Signal options (shared by `signal!`, `event!`, ...):

`:inst`  - Platform instant [1] when signal was created, ∈ #{nil :auto <user-val>}
`:level` - Signal level ∈ #{<int> :trace :debug :info :warn :error :fatal :report ...}
`:kind`  - Signal ?kind ∈ #{nil :event :error :log :trace :spy <user-val> ...}
`:id`    - ?id of signal call     (common to all signals created by signal call, contrast with `:uid`)
`:uid`   - ?id of signal instance (unique to each signal created by signal call, contrast with `:id`)

`:msg`   - Arb user-level ?message to incl. in signal: str or vec of strs to join (with `\space`)
`:data`  - Arb user-level ?data    to incl. in signal: usu. a map
`:error` - Arb user-level ?error   to incl. in signal: platform error [2]

`:run` - ?form    to execute UNCONDITIONALLY; will incl. `:run-value` in signal
`:do`  - ?form    to execute   conditionally (iff signal allowed), before establishing `:let` ?binding
`:let` - ?binding to establish conditionally (iff signal allowed), BEFORE evaluating `:data` and `:msg` (useful!)

`:ctx`      - Custom ?val to override auto (dynamic `*ctx*`) in signal
`:parent`   - Custom ?{:keys [id uid]} to override auto (dynamic) parent signal info in signal
`:location` - Custom ?{:keys [ns line column file]} to override auto signal call location

`:elidable?`   - Should signal call be subject to compile-time elision? (Default: true)
`:sample-rate` - ?rate ∈ℝ[0,1] for call sampling (0.75 => allow 75% of signals, nil => allow all)
`:when`        - Arb ?form; when present, form must return truthy to allow signal
`:rate-limit`  - ?spec as given to `telemere/rate-limiter`, see its docstring for details
`:middleware`  - ?[(fn [signal])=>modified-signal ...] call middleware
`:trace?`      - Should tracing be enabled for `:run` form?

<extra-kvs> - Arb user-level ?kvs to incl. in signal

If anything is unclear, please ping me (@ptaoussanis) so that I can improve these docs!

[1] `java.time.Instant`   or `js/Date`
[2] `java.lang.Throwable` or `js/Error`