Archive, multitagging, cleanup

Cleaned up the current snippets for consistency and minor problems, added multiple tags to most of them, archived a few.

snippets/sum.md

@@ -5,9 +5,9 @@ Returns the sum of two or more numbers/arrays.
 Use `Array.reduce()` to add each value to an accumulator, initialized with a value of `0`.
 
 ```js
-const sum = (...arr) => [].concat(...arr).reduce((acc, val) => acc + val, 0);
+const sum = (...arr) => [...arr].reduce((acc, val) => acc + val, 0);
 ```
 
 ```js
-sum([1, 2, 3, 4]); // 10
+sum(...[1, 2, 3, 4]); // 10
 ```