Improve multiline string diff about referee HOT 3 CLOSED

With #35 merged and published, I think this is significantly improved. I think we can close this

from referee.

I started looking into diff output, mainly because referee is not showing a very helpful error message when assert.equals fails on comparing two objects.

It seems like most test framewoks have a useful implementation for this based on expected and actual properties exposed on thrown errors. This is the way the Node assert module creates errors and maybe referee should do the same.

It makes sense to leave this to the test runner because there users can turn the behavior on or off and it might depend on the reporter in use to which level of detail and in which format the diff can be rendered (think console vs html vs json).

This would make the multilineStringDiff implementation entirely superfluous and also give us object diffs in a supporting framework.

I ran some quick checks with Mocha and it's relatively easy to make the change.
@mroderick What do you think?

from referee.

I like the idea of leaving it up to the test runner, as people will like things to be as homogenous in their chosen environments.

from referee.