function tap(value, interceptor) {
    interceptor(value);
    return value;
  }
Invokes `interceptor` with the `value` as the first argument, and then
returns `value`. The purpose of this method is to "tap into" a method chain,
in order to perform operations on intermediate results within the chain.

@static
@memberOf _
@category Chaining
@param {Mixed} value The value to pass to `interceptor`.
@param {Function} interceptor The function to invoke.
@returns {Mixed} Returns `value`.
@example

_.chain([1,2,3,200])
 .filter(function(num) { return num % 2 == 0; })
 .tap(alert)
 .map(function(num) { return num * num })
 .value();
// => // [2, 200] (alerted)
// => [4, 40000]