Call a Telemere signal creator to conditionally create a signal at that callsite.

When filtering conditions are met [4], the call creates a Telemere signal [3]
and dispatches it to registered handlers for processing (e.g. writing to
console/file/queue/db, etc.).

Telemere doesn't make a hard distinction between different kinds of signals
(log, event, error, etc.) - they're all just plain Clojure/Script maps with
various keys:

  - All signal creators offer the same options [2], and
  - All signal kinds can contain the same content [3]

Creators vary only in in their default options and call APIs (expected args
and return values), making them more/less convenient for certain use cases:

  `signal!` ------- opts            => allowed? / unconditional run result (value or throw)
  `event!` -------- id     + ?level => allowed?
  `log!` ---------- ?level + msg    => allowed?
  `trace!` -------- ?id    + run    => unconditional run result (value or throw)
  `spy!` ---------- ?level + run    => unconditional run result (value or throw)
  `error!` -------- ?id    + error  => unconditional given error
  `catch->error!` - ?id    + run    => unconditional run value or ?catch-val

- `log!` and `event!` are both good default/general-purpose signal creators.
- `log!` emphasizes messages, while `event!` emphasizes ids.
- `signal!` is the generic creator, and is used by all the others.

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[2] See `help:signal-options` - {:keys [kind level id data ...]}
[3] See `help:signal-content` - {:keys [kind level id data ...]}
[4] See `help:signal-filters` - (by ns/kind/id/level, sampling, etc.)