Docs: Restructuring and new layout

This patch implements a set of user-experiences aimed
changes.It modifies the documentation structure and
switches to a more reactive design for the rtd theme.

* The documentation layout has been redesigned to be more
  intuitive,easier to maintain and and scale.
* The landing page introduces a new dashboard.
* Introduced dedicated space for release documents, and
  changelog has been modified to directly source content
  from referenced documents.
* Added quick-link navigation for items that need emphasis.
* Relevant design documents can now be grouped in suf-folders.
* There is dedicated space for custom platform, and third
  party tools documents.
* Wildcard and regex matching has been introduced to indexes.

Change-Id: Ib02d17d5d26187d397ba17317788cf2a01401b07
Signed-off-by: Minos Galanakis <minos.galanakis@arm.com>
diff --git a/docs/_static/css/tfm_custom.css b/docs/_static/css/tfm_custom.css
new file mode 100644
index 0000000..909e2ac
--- /dev/null
+++ b/docs/_static/css/tfm_custom.css
@@ -0,0 +1,85 @@
+/*-----------------------------------------------------------------------------
+# Copyright (c) 2020, Arm Limited. All rights reserved.
+#
+# SPDX-License-Identifier: BSD-3-Clause
+#
+#----------------------------------------------------------------------------*/
+
+/* Expand width to fill screen */
+.wy-nav-content {
+   max-width: none;
+}
+
+/* Flexbox Tile Grid Settings  */
+.grid {
+    list-style-type: none !important;
+    display: -webkit-box;
+    display: -ms-flexbox;
+    display: flex;
+    -ms-flex-wrap: wrap;
+        flex-wrap: wrap;
+    -webkit-box-pack: center;
+        -ms-flex-pack: center;
+            justify-content: center;
+    margin: 1rem auto;
+    max-width: calc((250px + 2rem) * 4);
+}
+
+.grid-item {
+    list-style-type: none !important;
+    -webkit-box-flex: 0;
+        -ms-flex: 0 0 auto;
+            flex: 0 0 auto;
+    width: 220px;
+    text-align: center;
+    margin: 1rem;
+}
+
+.grid-item a {
+    display: block;
+    width: 220px;
+    height: 220px;
+    padding: 22px;
+    display: -webkit-box;
+    display: -ms-flexbox;
+    display: flex;
+    -webkit-box-orient: vertical;
+    -webkit-box-direction: normal;
+        -ms-flex-direction: column;
+            flex-direction: column;
+    -webkit-box-pack: center;
+        -ms-flex-pack: center;
+            justify-content: center;
+    -webkit-box-align: center;
+        -ms-flex-align: center;
+            align-items: center;
+    border: 1px solid #c6cbce;
+    background-color: #2980B9;
+    color: white;
+}
+
+.grid-item h2 {
+    font-size: 1.1rem;
+}
+
+.grid-item img {
+    margin-bottom: 1.1rem;
+    max-width: 75%;
+}
+
+.grid-item a:hover {
+    background-color: #32cd32;
+    color: white;
+}
+
+
+.grid-item p {
+    margin-top: 0.5rem;
+    color: #333e48;
+}
+
+.grid-icon {
+   line-height: 1.8;
+   font-size: 6rem;
+   color: #343131;
+}