Perform port normalization for http, https, ws, wss, and ftp schemes.

[lovelydinosaur]

Normalize the port component of URLs, so that...

assert httpx.URL("http://www.example.com") == httpx.URL("http://www.example.com:80")
print(httpx.URL("http://www.example.com:80"))  # URL('http://www.example.com')

Following this part of the WHATWG spec...

If url’s port is url’s scheme’s default port, then set url’s port to null.

And using the set of default ports as defined by https://url.spec.whatwg.org/#url-miscellaneous

I figure this probably helps iron away a few possible corner cases. It more neatly matches browser behaviour, and it's in line with other aspects of normalization that we're providing for, eg...

assert httpx.URL("http://WWW.EXAMPLE.COM") == httpx.URL("http://www.example.com")

It also has the nice property that url.netloc now properly encapsulates the same value that ought to be used for the value of the Host header.

[florimondmanca]

I'm happy enough with this. Thanks for the useful reference!