Module can destroy a record

**API**

```javascript
db.destroy(String|Array).then(function(){
  console.log("Success")
})
```

```javascript
describe("destroy", function() {

  it("should destroy a given record from its GUID", function() {
    var guid;

    return db.save({foo: "bar"})
      .then(function(id) {
        return guid = id
      })
      .then(db.destroy.bind(db))
      .then(function() {
        return db.get(guid)					// try to fetch the record again
      })
      .then(function(rec) {
        var res = rec === undefined	// rec should not exist
        res.should.be.true
      })
  })

  it("should destroy an array of given record GUIDs and return them", function() {
    var guids

    return db.save([ {foo: "bar"}, {bar: "foo"}])
      .then(function(ids) {
        return guids = ids
      })
      .then(db.destroy.bind(db))
      .then(function() {
        return db.get(guids)					// try to fetch the record again
      })
      .then(function(records) {			// values in array should be undefined
        records.every(function(record){ return record === undefined }).should.be.true
      })
    })
})
```