Generate a pseudo-random key that uniquely identifies easyPubMed
objects. The key is a 46-char string
that includes the current date + time and a list of
randomly selected characters, numbers and special characters.
The unique key is typically saved in the `meta` slot of an
easyPubMed object, and is also written to local files when
records are donwloaded and saved in XML format.
This function takes NO arguments.