Update collision doc.

doc/collisions.svg

@@ -0,0 +1,80 @@
+<?xml version="1.0" encoding="UTF-8" standalone="no"?>
+<!-- Created with Inkscape (http://www.inkscape.org/) -->
+
+<svg
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+   xmlns:cc="http://creativecommons.org/ns#"
+   xmlns:rdf="http://www.w3.org/1999/02/22-rdf-syntax-ns#"
+   xmlns:svg="http://www.w3.org/2000/svg"
+   xmlns="http://www.w3.org/2000/svg"
+   xmlns:xlink="http://www.w3.org/1999/xlink"
+   xmlns:sodipodi="http://sodipodi.sourceforge.net/DTD/sodipodi-0.dtd"
+   xmlns:inkscape="http://www.inkscape.org/namespaces/inkscape"
+   id="svg2"
+   version="1.1"
+   inkscape:version="0.47 r22583"
+   width="640"
+   height="352"
+   sodipodi:docname="collisions-bg.png">
+  <metadata
+     id="metadata8">
+    <rdf:RDF>
+      <cc:Work
+         rdf:about="">
+        <dc:format>image/svg+xml</dc:format>
+        <dc:type
+           rdf:resource="http://purl.org/dc/dcmitype/StillImage" />
+        <dc:title></dc:title>
+      </cc:Work>
+    </rdf:RDF>
+  </metadata>
+  <defs
+     id="defs6">
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+       sodipodi:type="inkscape:persp3d"
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+       inkscape:vp_y="0 : 1000 : 0"
+       inkscape:vp_z="1 : 0.5 : 1"
+       inkscape:persp3d-origin="0.5 : 0.33333333 : 1"
+       id="perspective10" />
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+  <sodipodi:namedview
+     pagecolor="#ffffff"
+     bordercolor="#666666"
+     borderopacity="1"
+     objecttolerance="10"
+     gridtolerance="10"
+     guidetolerance="10"
+     inkscape:pageopacity="0"
+     inkscape:pageshadow="2"
+     inkscape:window-width="1042"
+     inkscape:window-height="726"
+     id="namedview4"
+     showgrid="false"
+     inkscape:zoom="1.0030731"
+     inkscape:cx="267.48677"
+     inkscape:cy="130.98231"
+     inkscape:window-x="0"
+     inkscape:window-y="0"
+     inkscape:window-maximized="0"
+     inkscape:current-layer="svg2" />
+  <image
+     xlink:href="collisions-bg.png"
+     width="640"
+     height="352"
+     id="image12"
+     x="0"
+     y="0"
+     sodipodi:absref="collisions-bg.png" />
+  <text
+     xml:space="preserve"
+     style="font-size:16px;font-style:normal;font-variant:normal;font-weight:bold;font-stretch:normal;text-align:start;line-height:125%;writing-mode:lr-tb;text-anchor:start;fill:#000000;fill-opacity:1;stroke:none;font-family:Bitstream Vera Serif;-inkscape-font-specification:Bitstream Vera Serif Bold"
+     x="398.77454"
+     y="37.965061"
+     id="text2818"
+     sodipodi:linespacing="125%"><tspan
+       sodipodi:role="line"
+       id="tspan2820"
+       x="398.77454"
+       y="37.965061">Collision primitives</tspan></text>
+</svg>