add syscall article

templates/shortcodes/defref.html

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+<p id="ref{{ n }}">[{{ n }}] <a href="{{ url }}">{{ url }}</a> <a href="javascript:history.back()" style="text-decoration: none;">(↑)</a></p>

templates/shortcodes/note.html

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+<blockquote class="note">
+    {% set icon = load_data(path="static/images/info.svg") %}
+    <div class="icon">
+        {{ icon | safe }}
+    </div>
+    <div class="content">
+        {% if header %}
+        <p><strong>{{ header }}</strong></p>
+        {% endif %}
+        {{ body | markdown | safe }}
+    </div>
+</blockquote>

templates/shortcodes/ref.html

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+{% if not nosup %}<sup>{% endif %}<a href="#ref{{ n }}" style="text-decoration: none;">[{{ n }}]</a>{% if not nosup %}</sup>{% endif %}