New command 'describe-library'

New command 'describe-library'

* lisp/emacs-lisp/find-func.el
(find-library-include-other-files): Deprecate.
* lisp/emacs-lisp/find-func.el
(read-library-name-narrow-completions-by-keyword)
(find-func--finder-keyword-affixation)
(read-library-name-affixation): New functions.
(read-library-name): Add completions narrowing, annotations, and
a new argument PROMPT.
(display-library, find-library, find-library-other-window)
(find-library-other-frame)
* lisp/files.el (load-library)
* lisp/subr.el (locate-library): Use new PROMPT argument.
* lisp/help-mode.el (help-library-def): New button type.
* lisp/help-fns.el (describe-library): New command.
* lisp/help.el (help-map): Bind it to 'C-h C-l'.