Smart Key - Identifier Menu Mode

This works only for identifiers defined within the same source file in
which they are referenced.  It requires either Emacs’ imenu library
and it requires that an index of identifiers has been built for the
current buffer.  Other handlers handle identifier references and
definitions across multiple files.

When pressed on an identifier name after an identifier index has been generated:
  ACTION KEY
     Jumps to the source definition within the current buffer of the identifier at point.
  ASSIST KEY
     Prompts with completion for an identifier defined within the buffer and then jumps
     to the its source definition.