Complete doc string examples for functions.py (#1435)

* Verify all non-alias functions have doc string

* MNove all alias for statements to see also blocks and confirm no examples

* Fix google doc style for all examples

* Remove builtins use

* Add coverage for optional filter

* Cover optional argument examples for window and value functions

* Cover optional arguments for scalar functions

* Cover array and aggregation functions

* Make examples different

* Make format more consistent

* Remove duplicated df definition

Author: ntjohnson1