Do assertions dependant on call order

[kevinawoo]

This should resolve issues like #173 and #197 by letting the user determine which error should bubble up first.

Also added tests to validate ordering.

[mikelax]

@kevinawoo do you want to update this PR to resolve the conflicts? This would be nice to include in the next minor release.

[kevinawoo]

@mikelax sorry it took so long. All good to go.

[Rob--W]

You've introduced a stack of expectations to track order, while the separate arrays for bodies, (header) fields and status code are still kept. But the addition of the stack makes these arrays obsolete, so it's better to not confuse the reader and remove them.

Due to the size of the Test.prototype.assert function, it was not straightforward to reason about the correctness of the implementation. Therefore I submitted a new PR (#239) that fixes this issue and adds the feature (among a few others enhancements like this/res not being set and a superfluous instanceof Error check). I have cherry-picked your tests, because these appeared OK.

[kevinawoo]

Closed in favor of #239