Various docstring and commentary fixes, including

Various docstring and commentary fixes, including
note of current maintainer.
(fortran-mode): Use imenu-syntax-alist.
(fortran-imenu-generic-expression): Use
fortran-continuation-string, not always `+'.
(fortran-font-lock-keywords-1): Include symbol syntax as well
as word, following syntax table changes.
(fortran-imenu-generic-expression): Likewise.
(fortran-mode-map): Add a menu.
(fortran-mode-version, fortran-startup-message): Delete
misleading variables.
(fortran-mode): Don't use them.
(fortran-column-ruler-fixed, fortran-column-ruler-tab): Fix
leading \ which made `0' into null.
(fortran-join-lines): New function and key binding.
(fortran-narrow-to-subprogram): New function and key binding.
(fortran-mode-syntax-table): Make ?., ?_, ?$ symbol, not word.