Add EditorConfig support

Provide common indentation configuration for the source files.

For more information, visit https://editorconfig.org/.

Signed-off-by: Yegor Yefremov <yegorslists@googlemail.com>

.editorconfig

@@ -0,0 +1,11 @@
+root = true
+
+[*]
+end_of_line = lf
+trim_trailing_whitespace = true
+insert_final_newline = true
+
+[{*.c,*.h}]
+indent_style = space
+indent_size = 4
+tab_width = 4