update http links

- prefer https

- metadataworkinggroup.org/com seem to be offline; the web archive link
  was obtained from exiftool: https://exiftool.org/TagNames/MWG.html

- fix kramdown link, rubyforge has been gone a long time

- fix png/zlib links

Bug: webp:544
Bug: b/202302177
Change-Id: Id69de4553e7baf00393f12a2c1acb262443a1a93

iosbuild.sh

@@ -9,7 +9,7 @@
 # (the previous build will be erased if it exists).
 #
 # This script is inspired by the build script written by Carson McDonald.
-# (http://www.ioncannon.net/programming/1483/using-webp-to-reduce-native-ios-app-size/).
+# (https://www.ioncannon.net/programming/1483/using-webp-to-reduce-native-ios-app-size/).
 
 set -e
 
@@ -86,7 +86,7 @@ if [[ ! -e ${SRCDIR}/configure ]]; then
 Error creating configure script!
 This script requires the autoconf/automake and libtool to build. MacPorts can
 be used to obtain these:
-http://www.macports.org/install.php
+https://www.macports.org/install.php
 EOF
     exit 1
   fi