add editorconfig

Author: infctr

.editorconfig

@@ -0,0 +1,14 @@
+root = true
+
+[*]
+indent_style = space
+indent_size = 2
+max_line_length = 80
+end_of_line = lf
+charset = utf-8
+trim_trailing_whitespace = true
+insert_final_newline = true
+
+[*.md]
+max_line_length = 0
+trim_trailing_whitespace = false