Allow defs to be passed through to dot compile.

Pass down custom defines to templates, which doT.js allows but using with Consolidate.JS currently does not.  Small change.

Example:

| - test.js
| - views/home.html
| - views/main.html

```html
<!-- main.html -->
<html>
<body>
it.h at top of main.html = {{=it.h}}
<br/>
<br/>
{{#def.loadfile('./home.html')}}
</body>
<html>

<!-- home.html -->
<h1>it.h from within home.html = {{=it.h}}</h1>

```



```js

var fs = require('fs');
var dot = require('consolidate').dot;
var express = require('express');
var server = express();
var VIEWS = __dirname + '/views/';

server.set('views', VIEWS);
server.set('view engine', 'html' );
server.engine('html', dot );

server.get('/', function root(req,res) {

  var _def = {
    loadfile: function(path) {
      return fs.readFileSync(VIEWS + path);
    }
  };

  var options = {
    h: 'hi',
    _def: _def
  }

  res.render('main', options);
});
server.listen(8000);

```

localhost:3000/ returns:

```html
<html>
<body>
it.h at top of main.html = hi
<br/>
<br/>
<h1>it.h from within home.html = hi</h1>
</body>
<html>
```