remove "parse_host" API

[glyph]

What is the purpose of this API being public? It doesn't seem to connect with anything else in the docs.

[mahmoud]

It's a pretty simple function that might be of some utility. I don't feel very strongly about it, so I'm fine with removing it from the __init__.

[mahmoud]

Actually, on further reflection, there may be more to consider, toward the bottom of my comment here: #26 (comment)

[glyph]

APIs like this can have numerous sharp edges; understanding IPv6 is incredibly gnarly even at the best of times, and apparently-useful utilities like this can make it worse, so I'd be keen to avoid exposing it unless there's some reason that users really need it.