Warn if no assignment

[rjake]

These should have warnings bc missing assignment i.e. x <- load_reactive_objects(env = my_env())

see find_assign <- function() ... from http://adv-r.had.co.nz/Expressions.html

• [ ] load_reactive_objects(envir = new.env())
• [ ] "New" selected as environment from menu

https://stackoverflow.com/questions/54731759/how-to-detect-if-the-output-of-a-function-is-assigned-to-an-object-in-r