Add NuttX Online Demo

This PR adds the NuttX Online Demo based on [TinyEMU 64-bit RISC-V Emulator](https://github.com/fernandotcl/TinyEMU) and WebAssembly.

The [TinyEMU Port of NuttX](lupyuen2/wip-nuttx#54) shall be upstreamed later to NuttX Mainline. This will allow the Online Demo to be refreshed for new releases of NuttX. [More about NuttX for TinyEMU](https://lupyuen.github.io/articles/tinyemu)

Modified Files:

`index.md`: Add link to Demo Page: "Try the online demo here"

`_includes/themes/apache/default.html`: Add Demo CSS

New Files:

`demo.md`: New Demo Page with NuttX in TinyEMU Emulator

`demo/nuttx.bin`: NuttX Image compiled from the upcoming [TinyEMU Port of NuttX](lupyuen2/wip-nuttx#54) (64-bit RISC-V). Compiled with [these steps](https://github.com/lupyuen2/wip-pinephone-nuttx/releases/tag/tinyemu4-1) to produce these [Build Outputs](https://github.com/lupyuen2/wip-pinephone-nuttx/releases/tag/tinyemu4-1).

`demo/*.js, *.wasm, *.cfg, *.png`: Demo Files from [TinyEMU](https://github.com/fernandotcl/TinyEMU) project, based on [MIT Licence](https://github.com/fernandotcl/TinyEMU/blob/master/MIT-LICENSE.txt).

`assets/themes/apache/css/demo.css`: Demo CSS from [TinyEMU](https://github.com/fernandotcl/TinyEMU) project, based on [MIT Licence](https://github.com/fernandotcl/TinyEMU/blob/master/MIT-LICENSE.txt).

`_includes/themes/apache/demo.html`: New Theme for Demo Page

`_layouts/demo.html`: New Layout for Demo Page

_includes/themes/apache/default.html

@@ -18,6 +18,7 @@
     <link href="{{ site.baseurl }}/assets/themes/apache/bootstrap/css/bootstrap.css" rel="stylesheet">
     <link href="{{ site.baseurl }}/assets/themes/apache/css/style.css?body=1" rel="stylesheet" type="text/css">
     <link href="{{ site.baseurl }}/assets/themes/apache/css/syntax.css" rel="stylesheet"  type="text/css" media="screen" />
+    <link href="{{ site.baseurl }}/assets/themes/apache/css/demo.css" rel="stylesheet" type="text/css"/>
     <!-- Le fav and touch icons -->
     <!-- Update these with your own images
     <link rel="shortcut icon" href="images/favicon.ico">

_includes/themes/apache/demo.html

@@ -0,0 +1,22 @@
+<!--<div class="hero-unit {{ page.title | lowercase }}">
+  <h1>{% if page.tagline %} <small>{{ page.tagline }}</small>{% endif %}</h1>
+</div>
+-->
+
+<div class="row">
+  <div class="col-md-12">
+    {{ content }}
+
+    <div id="term_wrap">
+      <div id="term_container">
+      </div>
+      <div id="term_bar">
+        <progress id="net_progress">
+        </progress>
+      </div>
+    </div>  
+
+  </div>
+</div>
+<script type="text/javascript" src="/demo/term.js"></script>
+<script type="text/javascript" src="/demo/jslinux.js"></script>

_layouts/demo.html

@@ -0,0 +1,5 @@
+---
+layout: default
+---
+{% include JB/setup %}
+{% include themes/apache/demo.html %}

assets/themes/apache/css/demo.css

@@ -0,0 +1,105 @@
+#os_table {
+    border: 1px solid;
+    border-collapse: collapse;
+    margin: 20px;
+}
+
+#os_table td,#os_table th, #os_table tr {
+    border: 1px solid;
+    padding: 6px;
+}
+
+.os_comment {
+    font-size: 12px;
+}
+
+#copyright {
+    font-size: 10px;
+}
+
+/* for the terminal */
+#term_wrap {
+    margin: 20px;
+    resize: both;
+    overflow: hidden;
+}
+
+.term {
+    font-family: monospace,courier,fixed,swiss,sans-serif;
+    font-weight: normal;
+    font-variant-ligatures: none;
+    color: #f0f0f0;
+    background: #000000;
+    line-height: normal;
+    overflow: hidden;
+    white-space: nowrap;
+}
+
+.term_content a {
+    color: inherit;
+    text-decoration: none;
+}
+
+.term_content a:hover {
+    color: inherit;
+    text-decoration: underline;
+}
+
+.term_cursor {
+    color: #000000;
+    background: #00ff00;
+}
+
+.term_char_size {
+    display: inline-block;
+    visibility: hidden;
+    position: absolute;
+    top: 0px;
+    left: -1000px;
+    padding: 0px;
+}
+
+.term_textarea {
+    position: absolute;
+    top: 0px;
+    left: 0px;
+    width: 0px;
+    height: 0px;
+    padding: 0px;
+    border: 0px;
+    margin: 0px;
+    opacity: 0;
+    resize: none;
+}
+
+.term_scrollbar { background: transparent url(/demo/images/bg-scrollbar-track-y.png) no-repeat 0 0; position: relative; background-position: 0 0; float: right; height: 100%; }
+.term_track { background: transparent url(/demo/images/bg-scrollbar-trackend-y.png) no-repeat 0 100%; height: 100%; width:13px; position: relative; padding: 0 1px; }
+.term_thumb { background: transparent url(/demo/images/bg-scrollbar-thumb-y.png) no-repeat 50% 100%; height: 20px; width: 25px; cursor: pointer; overflow: hidden; position: absolute; top: 0; left: -5px; }
+.term_thumb .term_end { background: transparent url(/demo/images/bg-scrollbar-thumb-y.png) no-repeat 50% 0; overflow: hidden; height: 5px; width: 25px; }
+.noSelect { user-select: none; -o-user-select: none; -moz-user-select: none; -khtml-user-select: none; -webkit-user-select: none; }
+
+#keyboard-icon {
+    margin-left: 5px
+    margin-right: 5px;
+}
+
+/* file import */
+#files {
+    visibility: hidden;
+    width:1px;
+    height:1px;
+    padding: 0px;
+    margin: 0px;
+    border: 0px;
+}
+
+label {
+    cursor: pointer;
+    margin-left: 5px;
+    margin-right: 5px;
+}
+
+#net_progress {
+    visibility: hidden;
+    width: 80px;
+}

demo.md

@@ -0,0 +1,30 @@
+---
+layout: demo
+title: Demo
+tagline: Apache Project !
+---
+
+<!--
+{% comment %}
+Licensed to the Apache Software Foundation (ASF) under one or more
+contributor license agreements.  See the NOTICE file distributed with
+this work for additional information regarding copyright ownership.
+The ASF licenses this file to you under the Apache License, Version 2.0
+(the "License"); you may not use this file except in compliance with
+the License.  You may obtain a copy of the License at
+
+http://www.apache.org/licenses/LICENSE-2.0
+
+Unless required by applicable law or agreed to in writing, software
+distributed under the License is distributed on an "AS IS" BASIS,
+WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+See the License for the specific language governing permissions and
+limitations under the License.
+{% endcomment %}
+-->
+
+{% include JB/setup %}
+
+## NuttX Online Demo
+
+Enter `help` to see the available commands.