Allow specifying additional blocklevel, inline and empty tags for tidy

This allows specifying additional html5 tags for tidy to ignore.  For instance, while working with angular-ui, one can add the following: 

````
let g:syntastic_html_tidy_blocklevel_tags=["carousel", "slide"]
````

With frameworks like angularjs, one often adds new tags to html and this change allows us to have tidy ignore them.