Create faster low quality hash

[tkaitchuck]

Following up on rust-lang/hashbrown#207
It may be beneficial to have lower quality non-dos-resistant hash for cases where applications don't care about these features.

It would make sense to do this as a separate hasher instance. The trick is to find a way to do this without having to duplicate all of the code.

[tkaitchuck]

It may be better to have a separate HasherBuilder so that it can be changed on a map by map basis.

[colelawrence]

Would this make it more applicable to include meowhash? I think it has a similar approach to ahash.