[docs] added possibility for collapsing sections (#1594)

* added possibility to collapse long sections in docs

* added contents in the installation guide

docs/Installation-Guide.rst

@@ -5,6 +5,24 @@ Here is the guide for the build of LightGBM CLI version.
 
 For the build of Python-package and R-package, please refer to `Python-package`_ and `R-package`_ folders respectively.
 
+**Contents**
+
+-  `Windows <#windows>`__
+
+-  `Linux <#linux>`__
+
+-  `macOS <#macos>`__
+
+-  `Docker <#docker>`__
+
+-  `MPI Version <#build-mpi-version>`__
+
+-  `GPU Version <#build-gpu-version>`__
+
+-  `HDFS Version <#build-hdfs-version>`__
+
+-  `Java Wrapper <#build-java-wrapper>`__
+
 Windows
 ~~~~~~~
 

docs/_static/js/script.js

 $(function() {
     $('a[href^="./"][href*=".rst"]').attr('href', (i, val) => { return val.replace('.rst', '.html'); });  /* Replace '.rst' with '.html' in all internal links like './[Something].rst[#anchor]' */
-    $('.wy-nav-content').each(function () { this.style.setProperty('max-width', 'none', 'important'); });
+
+    $('.wy-nav-content').each(function () { this.style.setProperty('max-width', 'none', 'important'); });  /* Use wider container for the page content */
+
+    /* Collapse specified sections in the installation guide */
+    if(window.location.pathname.toLocaleLowerCase().indexOf('installation-guide') != -1) {
+        $('<style>.closed, .opened {cursor: pointer;} .closed:before, .opened:before {font-family: FontAwesome; display: inline-block; padding-right: 6px;} .closed:before {content: "\\f078";} .opened:before {content: "\\f077";}</style>').appendTo('body');
+        var collapsable = ['#build-mpi-version', '#build-gpu-version', '#build-hdfs-version', '#build-java-wrapper'];
+        $.each(collapsable, function(i, val) {
+            var header = val + ' > :header:first';
+            var content = val + ' :not(:header:first)';
+            $(header).addClass('closed');
+            $(content).hide();
+            $(header).click(function() {
+                $(header).toggleClass('closed opened');
+                $(content).slideToggle(0);
+            });
+        });
+        /* Uncollapse parent sections when nested section is specified in the URL or before navigate to it from navbar */
+        function uncollapse(section) {
+            section.parents().each((i, val) => { $(val).children('.closed').click(); });
+        }
+        uncollapse($(window.location.hash));
+        $('.wy-menu.wy-menu-vertical li a.reference.internal').click(function() {
+            uncollapse($($(this).attr('href')));
+        });
+    }
 });