Use spaces instead of tabs in files

.editorconfig:
Use spaces instead of tabs in files.
Add section for Makefile using tabs.

.editorconfig

@@ -3,6 +3,14 @@ root = true
 [*]
 end_of_line = lf
 charset = utf-8
+indent_style = space
+indent_size = 4
+insert_final_newline = true
+trim_trailing_whitespace = true
+
+[Makefile]
+end_of_line = lf
+charset = utf-8
 indent_style = tab
 indent_size = 4
 insert_final_newline = true