Add .editorconfig.

.editorconfig

@@ -0,0 +1,15 @@
+root = true
+
+[*]
+indent_size = 4
+indent_style = spaces
+end_of_line = lf
+charset = utf-8
+trim_trailing_whitespace = true
+insert_final_newline = true
+
+[*.go]
+indent_style = tab
+
+[file-extensions.txt]
+insert_final_newline = false