Fix bare ALD references being left as literal text

[PiotrCzapla]

What changed

Named attribute-list references used alone in an IAL will resolve after this pr.

This wasn't working previously:

{:note: #id .class}

Some text
{:note}

but this was fine

{:note: #id .class}

Some text
{:note .some-class}

Fix:
looks_like_attrs in src/attrs.rs gates whether a trailing {...} is treated as an attribute list, it recognizes it only if it containing #, ., or =, so pure note {:note} was ignored.

[jph00]

Thanks for the report and fix. looks_like_attrs was the right diagnosis. I ended up changing the rule instead of widening it: a braced group is an attribute list only when it starts with :, #, ., or a key=value pair. The colon form is always an attribute list, so {:note} and {: note} now resolve. Bare words like {note} stay literal even when defined, so an ALD name collision can't eat braced prose ({great note} would have silently dropped great). I modified your tests a bit based on these changes.
See #11