Feature request: add :to-error matcher

[diamond-lizard]

It would be nice if there was a :to-error matcher.

There's a :to-throw, but that's not quite the same.

There's should-error, but then you're not using the expect function.

For consistency with the other expect matchers, having a :to-error matcher would be appreciated.

[snogge]

What would :to-error do different from :to-throw?
The name :to-throw is unfortunate, it actually checks for signals raised by signal and error.
I'm considering renaming it to :to-signal, but maybe :to-error would be a better name. Obviously :to-throw would be kept as an alias.
Do we need a matcher to verify expressions that actually throws?

(I realise this answer is 3 years too late, but I'm trying to put in some work on buttercup again.)