Add .editorconfig
Add .editorconfig

This file is used by github to decide how to display things like
tab indentation.

It can also be used by a number of text editors and plug-ins to
aid with code formatting.

I have kept the tab indentation rules consistent with those set
in `.clang-format`.

See http://EditorConfig.org

MattSturgeon/OpenBoardView,chloridite/OpenBoardView,chloridite/OpenBoardView,MattSturgeon/OpenBoardView