Add ignore previous state flag

[clemencov]

Would be great to have same as crossroads.ignoreState flag to forced dispatch

[millermedeiros]

This would affect only hasher.setHash() because on IE 6-7 we pool for the current hash value to detect if it did change since last time.

This change is trivial and I agree that it could be useful in some cases, way easier to do it inside hasher itself than requiring some kind of wrapper/proxy. It might also be a motivator to do some cleanup in the code and abstract all the places that check the value of _hash (internal state, used to store previous/current hash value).

Right now I'm focusing on other projects so it might take a while, feel free to ask for a pull request in case you have time to do it. I will keep you posted in case I decide to work on this feature.

Thanks for the feedback.