Banning transient state by default

[Raynos]

Currently mercury allows transient state.

i.e. h('input') where you don't specify the value for the input and allow that state to live in the DOM as a mutable value.

This may cause subtle bugs like a virtual-dom diff / patch cycle not resetting the value to the empty string because it was left transient.

This is either a "feature" or a "bug".

One solution is to have mercury throw an exception if the user "accidentally" uses transient state and to make transient state opt in with something like h('input', { value: h.TRANSIENT })

[Raynos]

cc @Matt-Esch

[jxson]

The subtleties here seem like it would be better to have mercury throw in this case. I think most who get into this situation would probably get there on accident...