ex10.js

/*
SPY

Override a specified method of an object with new functionality while still maintaining all of the old behaviour.

Create a spy that keeps track of how many times a function is called.

## Example

    var spy = Spy(console, 'error')
    
    console.error('calling console.error')
    console.error('calling console.error')
    console.error('calling console.error')
    
    console.log(spy.count) // 3

## Arguments

  * target: an object containing the method `method`
  * method: a string with the name of the method on `target` to spy on.

## Conditions

  * Do not use any for/while loops or Array#forEach.
  * Do not create any unnecessary functions e.g. helpers.

## Hint

  * Functions have context, input and output. Make sure you consider the context, input to *and output from* the function you are spying on.

*/