Changed the .eds_message() operator, which I now think was a bad idea, to the .if_singular() operator.

The .if_singular() operator is a first in that it accepts arguments.
Changed templates in templates/ folder to use the new '.if_singular()' operator.
Changed tests in testing suite to use an unbreakable space '~' inside the 'etal_message'.
Changed testing suite BST files to use the new '.if_singular()' operator.
Starting long-needed revisions of documentation.