Allow for optional whitespace preservation

This would allow for a grunt configuration such as:

```javascript
var path = require("path");

module.exports = function (grunt) {
  //...
  grunt.loadNpmTasks("grunt-dustjs");
  //...

  var config = {
    //...
    dustjs: {},
    //...
  };

  config.dustjs: {
    compile: {
      files: {
        "js/templates.js": ["src/templates/**/*.html"]
      },
      options: {
        preserveWhitespace: true
      }
    }
  },
});
```


This is useful for cases where both `<script>` tags and `markdown` conversions require whitespace.