WIP: add oneway arrows to _all_ lines

assets/png/oneway.svg

@@ -0,0 +1,47 @@
+<?xml version="1.0" encoding="UTF-8" standalone="no"?>
+<svg
+   width="394.39307"
+   height="391.37128"
+   viewBox="0 0 394.39307 391.37128"
+   version="1.1"
+   id="svg1"
+   sodipodi:docname="oneway.svg"
+   inkscape:version="1.3.2 (091e20e, 2023-11-25)"
+   inkscape:export-filename="oneway.png"
+   inkscape:export-xdpi="96"
+   inkscape:export-ydpi="96"
+   xmlns:inkscape="http://www.inkscape.org/namespaces/inkscape"
+   xmlns:sodipodi="http://sodipodi.sourceforge.net/DTD/sodipodi-0.dtd"
+   xmlns="http://www.w3.org/2000/svg"
+   xmlns:svg="http://www.w3.org/2000/svg">
+  <defs
+     id="defs1" />
+  <sodipodi:namedview
+     id="namedview1"
+     pagecolor="#efe1c6"
+     bordercolor="#666666"
+     borderopacity="1.0"
+     inkscape:showpageshadow="2"
+     inkscape:pageopacity="0.0"
+     inkscape:pagecheckerboard="0"
+     inkscape:deskcolor="#d1d1d1"
+     inkscape:zoom="1.5375607"
+     inkscape:cx="170.07459"
+     inkscape:cy="205.52035"
+     inkscape:window-width="1850"
+     inkscape:window-height="1016"
+     inkscape:window-x="70"
+     inkscape:window-y="27"
+     inkscape:window-maximized="1"
+     inkscape:current-layer="svg1"
+     showgrid="false" />
+  <g
+     id="surface1"
+     transform="rotate(90,189.69566,197.95776)">
+    <path
+       style="fill:#000000;fill-opacity:1;fill-rule:nonzero;stroke:#ffffff;stroke-width:20;stroke-linecap:round;stroke-linejoin:bevel"
+       d="M 187.80469,0 375.40803,374.83557 187.60156,294.06641 94.257812,334.53516 C 42.917969,356.78906 0.3535155,374.31054 0.3535155,374.31054 Z"
+       id="path1"
+       sodipodi:nodetypes="cccccc" />
+  </g>
+</svg>