Add basic EditorConfig file

[jbampton]

https://editorconfig.org/

From the site:

"EditorConfig helps maintain consistent coding styles for multiple developers working on the same project across various editors and IDEs.
The EditorConfig project consists of a file format for defining coding styles and a collection of text editor plugins that enable editors to read the file format and adhere to defined styles.
EditorConfig files are easily readable and they work nicely with version control systems."

Most editors / IDEs are supported

[jbampton]

There is a good list of projects using EditorConfig:

https://github.com/editorconfig/editorconfig/wiki/Projects-Using-EditorConfig

[ardovm]

I suggest we add:
tab_width = 4
to the [*] section because many files are formatted this way.

A page on our wiki suggests to use 4 spaces for indentation, so we could also add:

indent_style = space
indent_size = 4

to the same section.

[Pilot-Pirx]

Wiki is often outdated.

Would that correspond to:

/* vim: set noet sw=4 ts=4: */

[ardovm]

Wiki is often outdated.

...but I liked it that way... ;-)

In fact, I thought that that wiki page was written after many files were already formatted with tabs.

It may be worth a short discussion on dev@.

Would that correspond to:

/* vim: set noet sw=4 ts=4: */

This should represent the current state of many files, i.e. tabs, to be displayed as 4 spaces.

I was suggesting we rather set et instead of noet, using no tabs for indentation, but rather 4 spaces.

[ardovm]

Wiki is often outdated.

Would that correspond to:

/* vim: set noet sw=4 ts=4: */

I looked further and now I agree that this is our current standard. Yes, the wiki is outdated.

So this PR shall only add:

tab_width = 4