Add interactive router doc, from Tomasz Wlostowski (see github.com/twlostow/kicad-dev/blob/junk/Documentation/interactive_router)

Remove the outdated pns_router.txt file.

Documentation/interactive_router/build.sh

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+#!/bin/bash
+
+pandoc -f markdown_mmd -t html interactive_router.mmd > interactive_router.html
+pandoc -f markdown_mmd -t latex interactive_router.mmd > tmp.tex
+pdflatex interactive_router.tex

Documentation/interactive_router/interactive_router.mmd

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+# Interactive Router #
+
+The Interactive Router lets you quickly and efficient route your PCBs by shoving off or walking around items on the PCB that collide with the trace you are currently drawing.
+
+Following modes are supported:
+
+- **Shove**, attempting to push and shove all items colliding with the currently routed track.
+- **Walk around**, trying to avoid obstacles by hugging/walking around them.
+- **Highlight collisions** which highlights all violating objects with a nice, shiny green color and shows violating clearance regions.
+
+
+## Setting up  ##
+
+Before using the Interactive Router, please set up these two things:
+- Clearance settings. To set the clearances, open the *Design Rules* dialog and make sure at least the default clearance
+value looks sensible.
+
+- Enable OpenGL mode by selecting *View->Switch canvas to OpenGL* menu option or pressing **F11**.
+
+![Screenshot](pictures/opengl_menu.png)
+
+## Laying out tracks ##
+
+To activate the router tool press the *Interactive Router* button ![Interactive Router Button](pictures/route_icon.png) or the **X** key.
+The cursor will turn into a cross and the tool name, will appear in the status bar.
+
+To start a track, click on any item (a pad, track or a via) or press the **X** key again hovering the mouse over that item.
+The new track will use the net of the starting item. Clicking or pressing **X** on empty PCB space starts a track with no net assigned.
+
+Move the mouse to define shape of the track. The router will try to follow mouse trail, hugging unmovable obstacles
+(such as pads) and shoving colliding traces/vias, depending on the mode. Retreating mouse cursor will cause the shoved items to spring back
+to their former locations.
+
+Clicking on a pad/track/via in the same net finishes routing. Clicking in empty space fixes the segments routed so far and continues routing the trace.
+
+In order to stop routing and undo all changes (shoved items, etc.), simply press **Esc**.
+
+Pressing **V** or selecting *Place Through Via* from the context menu while routing a track attaches a via at the end of the trace being routed.
+Pressing **V** again disables via placement. Clicking in any spot establishes the via and continues routing.
+
+Pressing **/** or selecting *Switch Track Posture* from the context menu toggles the direction of the initial track segment between straight or diagonal.
+
+**Note**: By default, the router snaps to centers/axes of the items. Snapping can be disabled by holding **Shift** while routing or selecting items.
+
+## Setting track widths and via sizes ##
+
+There are several ways to pre-select a track width/via size or to change it during routing:
+- Use standard Kicad shortcuts.
+- Press **W** or select *Custom Track Width* from the context menu to type in a custom width/via size.
+- Pick a predefined width from the *Select Track Width* sub-menu of the context menu.
+- Select *Use the starting track width* in the *Select Track Width* menu to pick the width from the start item (or the traces already connected to it).
+
+## Dragging ##
+
+The router can drag track segments, corners and vias. To drag an item, click on it with **Ctrl** key pressed, hover the mouse and press **G** or select *Drag Track/Via* from the context menu.
+Finish dragging by clicking again or abort by pressing *Esc*.
+
+## Options ##
+
+The router behavior be configured by pressing *E* or selecting *Routing Options* from the context menu. It opens a window like the one below:
+
+![Screenshot](pictures/router_options.png)
+
+The options are:
+
+- **Mode** - select how the router handles DRC violation (shoving, walking around, etc.)
+- **Shove vias** - when disabled, vias are treated as un-movable objects and hugged instead of shoved.
+- **Jump over obstacles** - when enabled, the router tries to move colliding traces behind solid obstacles (e.g. pads) instead of "reflecting" back the collision
+- **Remove redundant tracks** - removes loops while routing (e.g. if the new track ensures same connectivity as an already existing one, the old track is removed). Loop removal works locally (only between the start and end of the currently routed trace).
+- **Automatic neckdown** - when enabled, the router tries to break out pads/vias in a clean way, avoiding acute angles and jagged breakout traces.
+- **Smooth dragged segments** - when enabled, the router attempts to merge several jagged segments into a single straight one (dragging mode).
+- **Allow DRC violations** (*Highlight collisions* mode only) - allows to establish a track even if is violating the DRC rules.
+- **Optimizer effort** - defines how much time the router shall spend optimizing the routed/shoved traces. More effort means cleaner routing (but slower), less effort means faster routing but somewhat jagged traces.

Documentation/pns_router.txt

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-So, finally we've got an integrated interactive, push-and-sometimes-shove router, although with a very limited user interface:
-
-- Edit->Interactive router launches the tool,
-- while routing: 'V' key places a via,
-- '+' and '-' keys cycle through available layers,
-- '/' key switches track posture.
-
-Via/track dimensions are taken from the netclasses. 
-There are no other options available for the time being - promise to add them soon :)
-
-Tom