Low-level generic signal creator.

API: [opts] => depends on options [2]
Default  kind: none (optional)
Default level: none (must be provided)

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

If `:run` option is provided: returns value of given run form, or throws.
                   Otherwise: returns true iff signal was created (allowed).

Generic signals are fairly low-level and useful mostly for library authors or
advanced users writing their own wrapper macros. Regular users will typically
prefer one of the higher-level signal creators optimized for ease-of-use in
common cases [1].

Tips:

  - Test using `with-signal`: (with-signal (signal! ...)).
  - Supports the same options [2] as other signals [1].

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[1] See `help:signal-creators` - (`signal!`, `log!`, `event!`, ...)
[2] See `help:signal-options`  - {:keys [kind level id data ...]}
[3] See `help:signal-content`  - {:keys [kind level id data ...]}
[4] See `help:signal-flow`     - (filters, handling, etc.)