More cautious attempt to update docs

docs/intro.md

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+# Tanks Introduction 
+
+<figure>
+  <figcaption>"ChashTank" dominates this short round.</figure>
+  <canvas id="shortround"></canvas>
+  <script type="text/javascript">
+    start("shortround", shortround);
+  </script>
+</figure>
+
+Tanks is a game in which you pit your coding abilities against
+other hackers.  You write a program for your tank, set it out on
+the battlefield, and watch how it fares against other tanks while
+running your program.
+
+Each tank has a turret-mounted laser, two treads, up to ten
+sensors, and a diagnostic LED.  Sensors are used to detect when
+other tanks are inside a given arc.  In the examples on this page,
+"triggered" sensors turn black.  Most tanks will take some action
+if a sensor is triggered, such as changing speed of the treads,
+turning the turret, or firing.
+
+Tanks are programmed in Forf, a stack-based language similar to
+PostScript.  Please read the [Forf manual](forf.md) to learn more
+about forf, and the [Tanks procedure reference](procs.html) for a
+description of Tanks extensions.
+
+## Quick Start for the Impatient
+
+<figure>
+  <figcaption>"Crashmaster" pwns the lame default tank provided in this
+  section.</figcaption>
+  <canvas id="default"></canvas>
+  <script type="text/javascript">
+    start("default", default_);
+  </script>
+</figure>
+
+To get started, head over to the designer for your game,
+and use the following example tank.  This tank will
+move around, turn the turret, and fire if there's something in
+front of it.
+
+    Sensor 0: 50 0 7 ☑
+    Sensor 1: 30 0 90 ☐
+
+    get-turret 12 + set-turret!         ( Rotate turret )
+    37 40 set-speed!                    ( Go in circles )
+    0 sensor? { fire! } if              ( Fire if turret sensor triggered )
+    1 sensor? { -50 50 set-speed! } if  ( Turn if collision sensor triggered )
+
+Obviously, this tank could be improved.  
+Watch other tanks in your game to get ideas about how to improve yours.
+Don't forget the [Forf manual](forf.md) and the
+[Tank procedure reference](procs.html).
+
+## Tank Specifications
+
+<figure>
+  <figcaption>"Ant Lion" nails "Rabbit With Gun".</figcaption>
+  <canvas id="antlion"></canvas>
+  <script type="text/javascript">
+    start("antlion", antlion);
+  </script>
+</figure>
+
+Your PF-255 autonomous tank is built to the exacting
+specifications sent to our factory in New Khavistan.  All
+distances are in meters, angles in degrees.
+
+
+Tank size
+: The targettable area of the tank—the part which can be hit by a cannon—is a circle about 7½ meters in radius.
+
+Speed
+: Each tread can have a speed between -100 and 100.  This is in
+  percentage of total speed for that tread, where total speed is
+  roughly 7 meters per turn.
+
+Sensors
+: Each sensor has a maximum range of 100 meters.  Of course, you
+  don't have to use the full range.  Sensors may be attached to
+  the turret (they turn along with the turret), or left fixed to
+  the tank.
+
+Turret
+: Turret angle can be set between -359° and 359°, with 0° directly
+  in front of the tank.  Be aware that it takes time for the
+  turret to swing around: the turret can swing about 45° per turn.
+
+Cannon range and recharging
+: When the cannon is fired, it obliterates everything for 50
+  meters in front of it.  It takes around 20 turns for your cannon
+  to recharge after it's been fired, so only shoot when you feel
+  like you're going to hit something.
+
+Good luck blowing everybody up!