HTML5 Doctype

Hi, great job on getting HTML5 support into Tidy!

Are there any plans on supporting the HTML5 doctype?  It seems that with doctype = "auto" Tidy should recognize this as an HTML5 doctype:

``` html
<!DOCTYPE html>
```

Alas, it gets converted to a 4.01 doctype:

``` html
<!DOCTYPE html PUBLIC "-//W3C//DTD HTML 4.01//EN">
```
