fix doc url

See: https://github.com/springmeyer/travis-coredump/blob/master/.travis.yml

Also use assertEquals(), since assertSame() tests for object identity.

Normalizing top-level documents as arrays will allow single and multi-document checks to be more flexible. This will not extend to embedded documents, where we'll still need to be explicit.

Additionally, assertSameDocuments can now operate on any array or Traversable without needing to set its own type map.