update setup.py and fix #95: don't add slashes to void elements

[sknebel]

combined with setup.py since it relies on features new to BS4.

[sknebel]

concern with this: might break granary: https://github.com/microformats/mf2py/issues/95#issuecomment-427440995

[sknebel]

per further discussion in #95, granary can handle this by changing to html format in the Atom feeds

[kartikprabhu]

looks good to me. Might want to add some tests for this so that we can track any future changes to the code base.

[fluffy-critter]

Is there a reason why the MinimalHtmlFormatter uses class variables for configuration instead of instance variables assigned on __init__? And shouldn’t the subclass use __init__ regardless?

[fluffy-critter]

Also: From the BeautifulSoup documentation it looks like they already provide an HTML5 formatter which you get by passing the string"html5" to the formatter parameter