Make `@test test_reference` the API

[oxinabox]

A significant problem with the current API is that using @test_reference means we can't do @test_broken @test_reference

But we could do that if we made the test_reference function the API,
and have it returning true or false rather than doing @test true and error(...).

We can keep the current @test_reference for backwards compatibility, via it just generating the @test test_reference(...).

[oxinabox]

This would also make our tests much cleaner since we will be able to just @test !test_reference(...)

[oxinabox]

this would be closed by #112