Create a CanSimpleDocument constructor
Create a CanSimpleDocument constructor

This is needed so you can do: `new document.constructor()` which will
set up both the parser and serializer behavior. Currently in can-ssr we
are setting this up ourselves, which is gross:
https://github.com/canjs/can-ssr/blob/c5e2ec1be5cc28e1d6482b986f67c068dc4cc5b9/lib/index.js#L58

gsmeets/canjs,bitovi/canjs,tracer99/canjs,bitovi/canjs,tracer99/canjs,gsmeets/canjs,tracer99/canjs,bitovi/canjs,gsmeets/canjs,bitovi/canjs