Support passing custom css / js tags

I need to output

```html
<p:style>...</p:style>
```

instead of the usual

```html
<style></style>
```

This pull request adds two options, show here with their defaults:

```js
cssTags: {
  start: '<style>',
  end: '</style>' 
},
jsTags: {
  start: '<script>',
  end: '</script>'
}
```