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Remove the outdated pns_router.txt file.

fix Bug #1345193:  Drill Map coordinates alway 0 when using Gerber format (due to a missing plotter initialization).

Fix crash in Pcbnew and Gerbview when selecting (in layers manager) "always hide all layers but active" from popup menu

Fix crash in Pcbnew and Gerbview when seceting (in layers manager) "always hide all layers but activer"

Apply a workaround to fix a wxWidgets  bug in versions 3.0.x relative to mouse wheel event (Windows specific).
Therefore wxWidgets 3.0.1 can be used without need to patch it.
(This bug is fixed in wxWidgets 3.1)

Better separation between Pcbnew code and Gerber code.
Update export to Pcb code (uses now the version 4  kicad_pcb file format).

Gerbview: allows x.7 format (recently indroduced in Gerber format)
Also minor coding style fixes.

Gerbview: allows x.7 format (recently indroduced in Gerber format)
Also minor coding style fixes.