Allow both functions to incorporate time as a variable

[mattysimonson]

This will be a bit tricky but ideally you'd like to be able to feed in a data.frame and not a survey object. For now though, just create another wrapper that will allow it to recognize whether it is receiving a single tbl_srv or a list. As an intermediate step, maybe you can free it from its dependence on srvyr and just let it rely on survey since that's better known.