Add a predicate, color-dark-p, for deciding whether a colour is more
readable with black or white as contrast.  It has experimentally been
shown to be more accurate and robust than the various methods
currently employed.

The new predicate compares the relative luminance of the colour to an
empirically determined cut-off value, and it seems to get it right in
almost all cases, with no value leading to outright bad results.

* lisp/faces.el (readable-foreground-color): Use color-dark-p.
(color-dark-p): New function.
* lisp/facemenu.el (list-colors-print): Use readable-foreground-color,
improving readability of list-colors-display.
* lisp/textmodes/css-mode.el (css--contrasty-color): Remove.
(css--fontify-region): Use readable-foreground-color.

* doc/misc/tramp.texi (Top, Configuration): Insert section
`Keeping files encrypted' in menu.
(Keeping files encrypted): New node.

* lisp/net/tramp-crypt.el (tramp-crypt-file-name-handler-alist):
Add `tramp-set-file-uid-gid'.
(tramp-crypt-maybe-open-connection): Simplify.
(tramp-crypt-do-encrypt-or-decrypt-file): Use `binary' coding system.
(tramp-crypt-handle-set-file-uid-gid): New defun.

* test/lisp/net/tramp-tests.el (tramp-test09-insert-file-contents):
Adapt test.

* lisp/emacs-lisp/cl-macs.el (cl-lambda-list, cl-lambda-list1)
(cl-macro-list, cl-macro-list1): Use exactly the same specification as
for &optional (sans the third optional list element).

* lisp/emacs-lisp/cl-macs.el (cl-lambda-list, cl-lambda-list1)
(cl-macro-list, cl-macro-list1): Allow arbitrary 'cl-lambda'
arguments in the &aux section.

* test/lisp/emacs-lisp/cl-macs-tests.el (cl-macs-aux-edebug): New
regression test.

* lisp/progmodes/project.el (project--read-project-list): We are
already at BOB after insert-file-contents.

Save the project list file as lisp data instead of line separated
strings to make it more extendable in the future.

* lisp/progmodes/project.el (project--read-project-list)
(project--write-project-list, project--add-to-project-list-front)
(project--remove-from-project-list): Adjust to `project--list' now
being an alist.

* etc/NEWS: Correct the spelling of CC Mode.

* lisp/progmodes/cc-fonts.el (doxygen-font-lock-doc-comments): Replace curly
  quotes in comments by ASCII ones.