docs: Update references to Meson CLI utilities

The separate `mesonconf` and `mesontest` binaries have been deprecated,
in favour of `meson` sub-commands.

README.md

@@ -84,7 +84,7 @@ $ ninja
 You can run the test suite using:
 
 ```sh
-$ mesontest
+$ meson test
 ```
 
 And, finally, you can install GTK+ using:

docs/RELEASE-HOWTO.md

@@ -54,7 +54,7 @@ $ ninja -C _build gtk40-properties-pot
      release. **Note**: this is critical, a slip-up here will cause the soname
      to change.
 
-  6. Make sure that `mesontest` is happy (`ninja dist` will also run the test
+  6. Make sure that `meson test` is happy (`ninja dist` will also run the test
      suite, but it's better to catch issues before committing and tagging
      the release). Typical problems to expect here (depending on whether this
      is a devel  snapshot or a stable release):

docs/reference/gtk/building.sgml

@@ -56,7 +56,7 @@ How to compile GTK+ itself
     </para>
     <para>
       You can get a list of all available options for the build by
-      running <application>mesonconf</application>.
+      running <application>meson configure</application>.
     </para>
     <para>
       After Meson successfully configured the build directory, you then