Add EditorConfig to the repo.

Signed-off-by: Antonis Kalipetis <akalipetis@gmail.com>

.editorconfig

+root = true
+
+[*]
+indent_style = space
+indent_size = 4
+insert_final_newline = true
+trim_trailing_whitespace = true
+max_line_length = 80
+
+[*.md]
+trim_trailing_whitespace = false