Add editorconfig and normalize indent

Author: SamyPesse

.editorconfig

@@ -0,0 +1,10 @@
+# editorconfig.org
+root = true
+
+[*]
+indent_style = space
+indent_size = 4
+end_of_line = lf
+charset = utf-8
+trim_trailing_whitespace = true
+insert_final_newline = true