Add editorconfig file

.editorconfig

+# top-most EditorConfig file
+root = true
+
+[*]
+indent_size = 4
+indent_style = space
+charset = utf-8
+end_of_line = lf
+max_line_length = 100
+trim_trailing_whitespace = true
+
+[*.{c,h}]
+indent_style = tab
+
+[Makefile,configure]
+indent_style = tab
+