Add entry.index and appHistory.canGoBack/canGoForward

[domenic]

Closes #6.

[frehner]

Do you think there would be a desire to allow navigateTo() (or a similarly-named method) to take in the index?

I think it's not a big deal if it doesn't though (e.g. appHistory.navigateTo(appHistory.entries[index].key) )

(maybe somewhat related to the discussion in #7 as well)

[domenic]

Interesting. I'm unsure... I do think the discussion in #7 is more grounded in real use cases. Indices are a bit fragile.

[frehner]

Do you think there would be a desire to allow navigateTo() (or a similarly-named method) to take in the index?

I think it's not a big deal if it doesn't though (e.g. appHistory.navigateTo(appHistory.entries[index].key) )

(maybe somewhat related to the discussion in #7 as well)

The more I think about this, the more I think it's not necessary - in any case where you have an entry's index you'll also have its key (right?). And like you mentioned, the indices are fragile.