[m-rev.] diff: convert mercury_glut README to Markdown

[Julien Fischer]

Convert mercury_glut README to Markdown.

extras/graphics/mercury_glut/README:
     Rename this file to README.md.

     Convert the contents of this file to Markdown.

     Delete the link to the opengl.org site which is now empty.

     Add a link to the freeglut site.

Julien.

diff --git a/extras/graphics/mercury_glut/README.md b/extras/graphics/mercury_glut/README.md
index 6eb3431a9..02b10e003 100644
--- a/extras/graphics/mercury_glut/README.md
+++ b/extras/graphics/mercury_glut/README.md
@@ -1,16 +1,18 @@
-This directory contains the package `mercury_glut'
-which is a Mercury binding to the GL utility toolkit (GLUT).
+Mercury GLUT Binding
+====================

-GLUT provides a (relatively) platform independent API for
-writing OpenGL applications.  It provides most of the system
-dependent bits, such as window management, that the OpenGL API doesn't.
+This directory contains the package `mercury_glut` which is a Mercury binding
+to the GL utility toolkit (GLUT).

-If freeglut is being used to provide GLUT then `mercury_glut' also
-provides a interface to a number of freeglut specific extensions.
+GLUT provides a (relatively) platform independent API for writing OpenGL
+applications.  It provides most of the system dependent bits, such as window
+management, that the OpenGL API does not.

-See <http://www.opengl.org/resources/libraries/glut.html> for further 
-details.
+If [freeglut](http://freeglut.sourceforge.net) is being used to provide GLUT
+then `mercury_glut` also provides an interface to a number of freeglut specific
+extensions.

-The Mmakefile includes instructions for building and installing the
-library on Linux based systems.  Users of MacOS X, should instead see
-the file Mmakefile.MacOSX for instructions on how to build the binding.
+The [Mmakefile](Mmakefile) includes instructions for building and installing
+the library on Linux based systems.  Users of macOS, should instead see the
+file [Mmakefile.MacOSX](Mmakefile.MacOSX) for instructions on how to build the
+binding.