Add failing test for linking @ in @names via autoLinkWithJSON

[timhaines]

If you use autoLinkWithJSON, only 'name' of @name is linked. The @ is not linked. According to Twitter's display requirements, the @ should be linked too.

[timhaines]

[jakl]

An intermediary fix is to use

twtxt.autoLink("My @name", { usernameIncludeSymbol: true })

And we can make this option the default going forward.

[timhaines]

autoLinkWithJSON("my @name", entities, { usernameIncludeSymbol: true }) works too. Awesome. This is a non-issue for us now, but yeah, it seems like updating the defaults to match your display requirements would make sense.

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