New format of AUTHORS file; list each

New format of AUTHORS file; list each
author name once followed by contributed and changed files.
Improve selection of entries to include in list, and generate list
of unrecognized entries indicating syntax errors in ChangeLog files.
(authors-coding-system): New variable.
(authors-many-files): Update doc string.
(authors-aliases): Change format. Now one entry with multiple
aliases per author.
(authors-valid-file-names, authors-renamed-files-alist)
(authors-renamed-files-regexps): New variables.
(authors-canonical-file-name): New function.  Validates that file
exists or occurs in one of the above lists.  Record unrecognized
file names in global authors-invalid-file-names list.
(authors-add): Change to record per-change counts.
(authors-canonical-author-name): Handle new format of
authors-aliases list.
(authors-scan-change-log): Rename FILE arg to LOG-FILE.
Change doc string to describe new entry format.
Only add author entries for valid file names.
(authors-print): Replace by authors-add-to-author-list.
(authors-add-to-author-list): New function which reorders
per-file entries and adds them to global authors-author-list.
(authors): Instead of authors-print to insert in *Authors* buffer,
use authors-add-to-author-list to reorder the list and then
insert result in *Authors* buffer with new format.
Generate *Authors Errors* compilation-mode buffer listing
unrecognized ChangeLog entries.