Add .editorconfig file

Add .editorconfig file

Many editors support reading this file to automatically configure indent
/ whitespace settings. The author of this patch would be extremely
grateful if the maintainer of the project would consider merging the
patch in the master branch of the project's repository.

Change-Id: I84ae62fe3e028d0d40421943b3a53207854efed7
Signed-off-by: Simon Marchi <simon.marchi@efficios.com>
Signed-off-by: Jérémie Galarneau <jeremie.galarneau@efficios.com>