Sticky machine and machine command controls are implemented in Jekyll now, too

_includes/machine-command.html

@@ -0,0 +1,16 @@
+{% comment %}
+
+As discussed in /_posts/2017-01-03-pdp-11-tutorials.md, when a page (usually part of a tutorial)
+wants to create a control that tests some feature of a machine, the page will define a machine command
+using a Liquid-style include that looks like:
+
+    {% include machine-command.html type='button' label='Try It!' machine='vt100' component='Keyboard' command='sendString' value='Hello World' %}
+
+and which should generate something like:
+
+    <button type="button" onclick="commandMachine('vt100','Keyboard','sendString','Hello World')">Try It!</button>
+
+Well, that's us.  So let's do it!
+
+{% endcomment %}
+{% if include.type == "button" %}<button type="button" onclick="commandMachine('{{ include.machine }}','{{ include.component }}','{{ include.command }}','{{ include.value }}')">{{ include.label }}</button>{% else %}<!-- Unrecognized machine control type: {{ include.type }} -->{% endif %}