don't parameterize [A|M|W]Form based on monad, instead use site

[mixphix]

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Greatly simplifies the type signatures and concretizes the monad in which things happen (namely HandlerFor site), but comes at the cost of no longer having MonadTrans AForm and potentially writing a few more liftHandlers.

The version numbers are suggestions, perhaps this is big enough to bump to 2.0, perhaps just to 1.8, I'll leave that to your discretion.

[parsonsmatt]

The change here is pretty significant and I don't see much benefit. While I do like this design more than the prior one, I'd need to be convinced that there's good reason to force all users to upgrade.