Use https links in more spots.

README.Docker:
README.bootstrap:
README.cross.md:
README.md:
RELEASE_NOTES:
     As above.

README.Docker

@@ -22,7 +22,7 @@ Currently there are three stages:
     it comes with gcc, make, pkg-config and libc headers.
 
   - bootstrap: Installs the packaged ROTD compiler from the
-    [download page](http://dl.mercurylang.org/deb/) and autotools.
+    [download page](https://dl.mercurylang.org/deb/) and autotools.
 
   - compiler: Uses the bootstrapped compiler to (auto-)configure Mercury and
     install it into a single-layered container.
@@ -57,7 +57,7 @@ Additionally building the ROTD tarball is supported via:
 ```bash
   docker build --build-arg MERCURY_BOOTSTRAP=n \
     --build-arg MERCURY_DEV_SOURCE=mercury-srcdist-rotd-2018-12-24 \
-    http://dl.mercurylang.org/rotd/mercury-srcdist-rotd-2018-12-24.tar.gz
+    https://dl.mercurylang.org/rotd/mercury-srcdist-rotd-2018-12-24.tar.gz
 ```
 
 Using containerised mmc on the host platform

README.bootstrap

@@ -17,7 +17,7 @@ recommended to start with the most recent ROTD release since older versions of
 the Mercury compiler are frequently not able to build the bleeding edge in Git.
 
 The releases can be downloaded from the Mercury website's downloads page:
-http://dl.mercurylang.org/index.html.
+https://dl.mercurylang.org/index.html.
 
 Other prerequisites can be found in relevant README.* files in the
 distribution's root directory.
@@ -63,7 +63,7 @@ option, where <grade list> is a comma separated list of grades.  For information
 about which grades may be relevant, see the documentation on grades and grade
 components:
 
-   http://www.mercurylang.org/information/doc-latest/mercury_user_guide/Grades-and-grade-components.html
+   https://www.mercurylang.org/information/doc-latest/mercury_user_guide/Grades-and-grade-components.html
 
 People wanting to simply experiment with Mercury would be best-served with
 using only the `asm_fast.gc` grade or `hlc.gc` on OS X.

README.cross.md

@@ -40,7 +40,7 @@ Instructions for GCC
       - gcc-mingw-w64-i686
       - gcc-aarch64-linux-gnu
 
-    Alternatively, you can use <http://mxe.cc/> to install a MinGW-w64
+    Alternatively, you can use <https://mxe.cc/> to install a MinGW-w64
     toolchain on Unix-like hosts.
 
     Whatever the means, you should have the C cross-compiler in your PATH,

README.md

@@ -1,14 +1,14 @@
 Mercury
 =======
 
-[Mercury](http://www.mercurylang.org/) is a logic/functional programming
+[Mercury](https://www.mercurylang.org/) is a logic/functional programming
 language which combines the clarity and the expressiveness of declarative
 programming with advanced static analysis and error detection features.
 
 More information is available on the
-[website's about pages](http://www.mercurylang.org/about.html),
+[website's about pages](https://www.mercurylang.org/about.html),
 in other README files in the source code repository, and in the
-[documentation](http://www.mercurylang.org/documentation/documentation.html).
+[documentation](https://www.mercurylang.org/documentation/documentation.html).
 
 Small sample programs written in Mercury can be found
 in the [samples](samples) and [extras](extras) directories
@@ -17,7 +17,7 @@ of the source code repository.
 ## README files
 
 The Mercury compiler has two different
-[backends](http://www.mercurylang.org/about/backends.html)
+[backends](https://www.mercurylang.org/about/backends.html)
 and works on different operating systems.
 Specific information is contained in individual README files:
 
@@ -73,10 +73,10 @@ in which the Mercury implementation does not yet meet its goals.
 If you are considering contributing to the Mercury project,
 the website contains some documents that may be helpful.
 These include a document about
-[contributions in general](http://www.mercurylang.org/development/contributions.html) and
-[specific information](http://www.mercurylang.org/development/developer.html)
+[contributions in general](https://www.mercurylang.org/development/contributions.html) and
+[specific information](https://www.mercurylang.org/development/developer.html)
 about contributing such as coding styles.
 
 ## Contact
 
-See [our contact page](http://www.mercurylang.org/contact.html).
+See [our contact page](https://www.mercurylang.org/contact.html).

RELEASE_NOTES

@@ -154,7 +154,7 @@ Mac OS X (PowerPC) and Windows 95, 98, ME, NT, 2000 and XP.
 
 It should run without too many changes on other Unix variants as well.
 If you do encounter any problems, please report them to us via the
-Mercury bug tracking system at <http://bugs.mercurylang.org>
+Mercury bug tracking system at <https://bugs.mercurylang.org>
 (see the BUGS file).
 
 We recommend that you use gcc as the C compiler, preferably gcc version 3.4 or
@@ -203,11 +203,11 @@ The Mercury distribution contains:
 The Mercury distribution is available via WWW from the following locations:
 
         Australia:
-                <http://dl.mercurylang.org/index.html>
+                <https://dl.mercurylang.org/index.html>
 
 The home page of the project on the Web is:
 
-    <http://www.mercurylang.org>.
+    <https://www.mercurylang.org>.
 
 --
-The Mercury Team <http://www.mercurylang.org/development/people.html>
+The Mercury Team <https://www.mercurylang.org/development/people.html>