Add .editorconfig

This is not a complete replacement for clang-format, but it'll at least
set people's tab widths correctly.

.editorconfig

@@ -0,0 +1,14 @@
+# To use this config on you editor, follow the instructions at:
+# http://editorconfig.org
+
+root = true
+
+[*]
+charset = utf-8
+insert_final_newline = true
+tab_width = 8
+
+[*.{c,h,cpp}]
+indent_style = tab
+indent_size = 8
+max_line_length = 80