Disallow = and : as bare items in [] containers, as that likely is
"[ { foo = bar } ]" mistyped as "[ foo = bar ]".
Disallow nesting errors, eg. "[ foo bar" or "[ foo bar }".
Fix handling of ", \ and # in bare strings.
Fix ignoring trailing comments.
Add a fixed-size stack (128 levels) to the tokenizer, so that it can
check these at levels below its depth.
When the tokenizer encounters an error, make it and its parents enter
error state where no further input will be processed. This allows caller
to check for parse errors later as convenient.
The error state can be queried using spa_json_get_error, which also
looks up the error line/column position.
