Issue title: return find result
 Issue body: How can I get the query's result outside of the `db.find` in a variable? Something like below:

```
var result = db.find({}, function (err, docs) {
 });

console.log(result);
```

 Comments: 
 Comment 0: @tokhi: You can assign it to an outer variable, like this:

``` javascript
var result;
db.find({}, function(err, docs) {
  result = docs[0];
});

console.log(result); // this will not be defined, since nedb is asynchronous and the callback won't have run yet

setTimeout(function() {
  console.log(result); // this will (probably) be defined, since nedb is fast & shouldn't take a full second
}, 1000);
```

You run into this kind of async programming stuff a lot with node.js, so there are lots of helps for async-programming in the node community and a variety of ways to deal with "callback hell" and the timing issues, like using straight callbacks, using a callback helper library like caolan's async, or using promises...

 Comment 1: I found this on stackoverflow and it works:

``` javascript
var x = null;
db.find({ }, function (err, docs) {
  x = docs;
  do_something_when_you_get_your_result();
});

function do_something_when_you_get_your_result() {
  console.log(x); // x have docs now
}
```

 Comment 2: @tokhi: Yep, doing something like that (a straight callback approach) works well. You could also tweak it slightly to pass the docs directly:

``` javascript
db.find({ }, function (err, docs) {
  if (err) throw err;
  do_something_when_you_get_your_result(docs);
});

function do_something_when_you_get_your_result(docs) {
  console.log(docs);
}
```

The main point being that an async operation like `db.find()` can't return the result immediately, it is only available later, when the callback function is executed.

Notice the `if (err) throw err` -- you'll want to check for the error and do something with it instead of ignoring it altogether (for initial development it's usually enough to just `throw` it, but later on you may want to suppress some errors or do something special to notify the user of the errors)

 Comment 3: @prust : Yep, thanks. :+1: 

{'source': 'GithubIssues', 'repo_name_with_owner': 'louischatriot/nedb', 'issue_id': 51625119, 'repo_stars': 13194.0}