Archive, multitagging, cleanup

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

snippets/average.md

@@ -1,17 +1,14 @@
 ### average
 
-Returns the average of an of two or more numbers/arrays.
+Returns the average of an of two or more numbers.
 
 Use `Array.reduce()` to add each value to an accumulator, initialized with a value of `0`, divide by the `length` of the array.
 
 ```js
-const average = (...arr) => {
-  const nums = [].concat(...arr);
-  return nums.reduce((acc, val) => acc + val, 0) / nums.length;
-};
+const average = (...nums) => [...nums].reduce((acc, val) => acc + val, 0) / nums.length;
 ```
 
 ```js
-average([1, 2, 3]); // 2
+average(...[1, 2, 3]); // 2
 average(1, 2, 3); // 2
 ```