You have been provided with a rich and valuable data-set that you
need to provide a simple query interface to.

In this exercise you will be given a LevelDB store that contains
over 2,000 tweets from [@horse_js](https://twitter.com/horse_js).
Your job is to query this dataset and return the number of tweets
that occur from a given date to the _end_ of the data set.

Each entry is a single tweet. The key is the exact time that the
tweet was sent, in standard ISO date format (i.e. the format
generated by the `Date` object's `toISOString()` method.) The value
of the entry is simply a String representing the tweet's content.

Write a **module** that exports a single function that
accepts three arguments: an instance of an existing LevelUP database,
a date string, of the form `YYYY-MM-DD` and a callback function.

The first argument returned on the callback should be an Error if one
occurred or null. The second argument, if there was no error, should
be an integer, representing the number of tweets since that date.

Your solution will be checked against the official solution to ensure
that your query is targeting the exact range (see details below).
The output will include the number of "streamed entries".

---

## Hints:

Use this boilerplate to get started with your module file:

```javascript
module.exports = function (databaseDir, date, callback) {
  // .. your code here
  callback(error, tweetCount)
}
```

The ISO date format will always sort lexicographically, which means
that our tweets appear in date/time order in our data store without
any special work required on your part.

In this exercise, you will need to use the `createReadStream()`
method but you will need to restrict the range of entries to just the
data you need, i.e. you must perform a "range query".

By default, the range is the whole store, but you can narrow it down
to a start and/or end key. For this exercise you want to start at
a particular date and continue to the end of the store.

Some of the power of range queries comes from the fact that your
start and end keys need not even exist. If your start key does not
exist then the data will start from the entry with a key that
would come next in the sorted order.

When you call `createReadStream()`, provide an options object with
the property 'gte' (greater than or equal). The value of this property can simply be the
original date string since YYYY-MM-DD is how the ISO format starts
and this will make the ReadStream jump to the first key that begins
with that prefix, i.e. the first tweet on that day.

```javascript
db.createReadStream({ gte: '...' })...
```

The rest of the solution will involve incrementing a counter for each
'data' event you receive and then returning the total count as the
second argument on the callback.