"Old" `poolmanager.proxy_from_url()`, instantiated `ProxyManager` with an `HTTPConnectionPool` instance:

```python
def proxy_from_url(url, **pool_kw):
    proxy_pool = connection_from_url(url, **pool_kw)
    return ProxyManager(proxy_pool) 
```

The changed code is preserving the API. I am happy to remove this rather confusing action if the author is happy.