(PUP-3001) Specify Resource Expression Operations

In PUP-3001, the change of not using dynamic scoping for
resource defaults was reversed, and this triggered the need to update
the specification (which had no text for this).

This commit also fixes unfinished parts of the specification in
modus-operandi, moves one section from catalog_expressions to 
modus_operandi (about auto loading).
(maint) Update the deprecations section (remove dead code, fix language)
(maint) Clean up func-api.doc

This removes stale comments / text.
(maint) Correct typo in explanation of set algebra

The word "not" was missing in an important place.
Add Puppet Heredoc specification (from ARM-4) and adjusted to impl.
(maint) Add links between places heredoc is covered