(Fortran): Change description of free form and

(Fortran): Change description of free form and
fixed form a bit.  Mention hideshow and imenu.
(Fortran Motion): Mention fortran-end-of-subprogram,
fortran-beginning-of-subprogram, fortran-mark-do, fortran-mark-if.
(Fortran Indent): Minor re-word.
(ForIndent Commands): Mention fortran-fill-paragraph and
fortran-fill-statement.
(ForIndent Cont): Mention fortran-tab-mode-string.
(Fortran Comments): Mention fortran-comment-line-start-skip.
(Fortran Columns): Mention font-locking.
(Fortran Abbrev): Word syntax not relevant with new-style abbrev.