Prefer HTTPS to FTP and HTTP in documentation

Most of this change is to boilerplate commentary such as license URLs.
This change was prompted by ftp://ftp.gnu.org's going-away party,
planned for November.  Change these FTP URLs to https://ftp.gnu.org
instead.  Make similar changes for URLs to other organizations moving
away from FTP.  Also, change HTTP to HTTPS for URLs to gnu.org and
fsf.org when this works, as this will further help defend against
man-in-the-middle attacks (for this part I omitted the MS-DOS and
MS-Windows sources and the test tarballs to keep the workload down).
HTTPS is not fully working to lists.gnu.org so I left those URLs alone
for now.

doc/lispref/tips.texi

@@ -741,7 +741,7 @@ preceded by @samp{URL}.  For example,
 
 @smallexample
 The home page for the GNU project has more information (see URL
-`http://www.gnu.org/').
+`https://www.gnu.org/').
 @end smallexample
 
 @item
@@ -944,7 +944,7 @@ explains these conventions, starting with an example:
 
 ;; This file is free software@dots{}
 @dots{}
-;; along with this file.  If not, see <http://www.gnu.org/licenses/>.
+;; along with this file.  If not, see <https://www.gnu.org/licenses/>.
 @end group
 @end smallexample
 
@@ -966,7 +966,7 @@ might need to list them instead.  Do not say that the copyright holder
 is the Free Software Foundation (or that the file is part of GNU
 Emacs) unless your file has been accepted into the Emacs distribution.
 For more information on the form of copyright and license notices, see
-@uref{http://www.gnu.org/licenses/gpl-howto.html, the guide on the GNU
+@uref{https://www.gnu.org/licenses/gpl-howto.html, the guide on the GNU
 website}.
 
   After the copyright notice come several @dfn{header comment} lines,