CSS transition helpers

[leeoniya]

it would be nice to have some declarative transition support in domvm. i'm not sure what the api should look like, maybe {_trans: }, or if it can be an external plugin that will just set up the proper hooks as i do in the ModalStack [1] demo [2]...which is not general enough, but some bits can be adopted perhaps.

api proposals and/or fiddles now being accepted!

http://johan-gorter.github.io/maquette-demo-hero/
https://github.com/zaceno/hyperapp-transitions
https://rawgit.com/snabbdom/snabbdom/master/examples/hero/index.html

cc @iamjohnlong @sabine

[1] https://github.com/leeoniya/domvm/blob/3.x-dev/demos/ModalStack/index.html
[2] https://cdn.rawgit.com/leeoniya/domvm/3.x-dev/demos/ModalStack/index.html

[lawrence-dol]

@leeoniya : I suggest enabling discussions and moving this to a discussion.