Differentiates arrays and objects

[jamesplease]

Start of a solution to #31.

This begins the process of differentiating between arrays and objects. The fix in this PR only compares empty ones, though. It'll likely take a different sort of refactor to handle all cases.

To test:

// On master, you get nothing.
jsonpatch.compare({a: {}}, {a: []});

// On this branch, you get a nice replace. Yippee

[warpech]

Are you still using this? Could you please add a test for it?

[jamesplease]

I'm not using it. Gonna close cause I won't have 🕰