Add LocalProtocolError, RemoteProtocolError

[lovelydinosaur]

Distinguish between local and remote protocol errors, so that we can expose local errors for invalid requests, eg...

>>>importhttpcore>>>http=httpcore.SyncConnectionPool()
>>>http.request(b"GET", (b'https', b'example.org', 443, b'/'))
Traceback (mostrecentcalllast):
File"<stdin>", line1, in<module>File"/Users/tomchristie/GitHub/encode/httpcore/httpcore/_sync/connection_pool.py", line153, inrequestmethod, url, headers=headers, stream=stream, timeout=timeoutFile"/Users/tomchristie/GitHub/encode/httpcore/httpcore/_sync/connection.py", line93, inrequestreturnself.connection.request(method, url, headers, stream, timeout)
File"/Users/tomchristie/GitHub/encode/httpcore/httpcore/_sync/http11.py", line61, inrequestself._send_request(method, url, headers, timeout)
File"/Users/tomchristie/GitHub/encode/httpcore/httpcore/_sync/http11.py", line88, in_send_requestevent=h11.Request(method=method, target=target, headers=headers)
File"/Library/Frameworks/Python.framework/Versions/3.7/lib/python3.7/contextlib.py", line130, in__exit__self.gen.throw(type, value, traceback)
File"/Users/tomchristie/GitHub/encode/httpcore/httpcore/_exceptions.py", line12, inmap_exceptionsraiseto_exc(exc) fromNonehttpcore._exceptions.LocalProtocolError: MissingmandatoryHost: header

And...

>>>importhttpcore>>>http=httpcore.SyncConnectionPool()
>>>http.request(b"GET", (b'https', b'', 443, b'/'))
Traceback (mostrecentcalllast):
File"<stdin>", line1, in<module>File"/Users/tomchristie/GitHub/encode/httpcore/httpcore/_sync/connection_pool.py", line130, inrequestraiseLocalProtocolError("Missing hostname in URL.")
httpcore._exceptions.LocalProtocolError: MissinghostnameinURL.

[florimondmanca]

Sweet!

I have a question - do we even need ProtocolError anymore? I don't think it's being used elsewhere in the package anymore. Edit: okay, ProtocolError is kept as the base class, that makes sense and I hadn't seen that. :-)