Ediff: add some missing documentation

Ediff: add some missing documentation

* vc/ediff.el (ediff-files, ediff-files3, ediff-buffers)
(ediff-buffers3, ediff-merge-directories)
(ediff-merge-directories-with-ancestor)
(ediff-merge-directory-revisions)
(ediff-merge-directory-revisions-with-ancestor)
(ediff-windows-wordwise, ediff-windows-linewise)
(ediff-regions-wordwise, ediff-regions-linewise)
(ediff-merge-files, ediff-merge-files-with-ancestor)
(ediff-merge-buffers, ediff-merge-buffers-with-ancestor)
(ediff-merge-revisions, ediff-merge-revisions-with-ancestor)
(ediff-patch-file, ediff-revision): Document missing arguments.
(ediff-patch-buffer, ediff-revision): Add second space after
period.
(ediff-files-command, ediff3-files-command, ediff-merge-command)
(ediff-merge-with-ancestor-command, ediff-directories-command)
(ediff-directories3-command, ediff-merge-directories-command): Add
documentation for the command line functions.