options: add notEncodeEntities

Added option `notEncodeEntities` which could be used to work with inline scripts and styles in `html` and `xml` functions.
Any way `this.options` which is used now is always `undefined` and have no sense.

This would fix #484 #460. I think it's little bit better than [this solution](https://github.com/cheeriojs/cheerio/pull/461).
For now I use this thing
```js
data = entities.decodeHTML($.html());
```
for inline styles and scripts in [minify](http://coderaiser.github.io/minify), but it's adds one more dependency and looks very bad. 

P.S.: Build failed because of `travis`.