Add EditorConfig file

I'm creating this pull request to open the discussion for adding an
EditorConfig file.

This file should help prevent problems such as the one fixed by #31.

If this change is too controversial (since it would generate a
.editorconfig file in each generated project), the file could be moved
one directory up.

Disclosure: I am biased in my appreciation for these files because I'm
one of the core maintainers of the EditorConfig project.