Add .editorconfig

Set various editor configuration values. This includes setting indent
type to tab characters, with each character set to 4-space size.

.editorconfig

@@ -0,0 +1,12 @@
+root = true
+
+
+[*]
+indent_style = tab
+indent_size = 4
+tab_width = 4
+end_of_line = lf
+charset = utf-8
+trim_trailing_whitespace = true
+insert_final_newline = true
+