.get should have options as the last argument

[msluther]

On the next breaking change, we should swap the order to make the optional options object be easier to work with.

Now:

myCache.get('foo', {}, myGetterFn);

Should become:

myCache.get('foo', myGetterFn, {});

that allows for making it more optional and dropping it altogether without having to typecheck anything:

this:

myCache.get('foo', void 0, myGetterFn);

becomes this:

myCache.get('foo', myGetterFn);