Initial python3 changes

Mostly just updating libraries, removing string encoding/decoding,
fixing some edge cases. No new functionality was added in this
commit.

lib/cheroot/cli.pyi

@@ -0,0 +1,32 @@
+from typing import Any
+
+class BindLocation: ...
+
+class TCPSocket(BindLocation):
+    bind_addr: Any
+    def __init__(self, address, port) -> None: ...
+
+class UnixSocket(BindLocation):
+    bind_addr: Any
+    def __init__(self, path) -> None: ...
+
+class AbstractSocket(BindLocation):
+    bind_addr: Any
+    def __init__(self, abstract_socket) -> None: ...
+
+class Application:
+    @classmethod
+    def resolve(cls, full_path): ...
+    wsgi_app: Any
+    def __init__(self, wsgi_app) -> None: ...
+    def server_args(self, parsed_args): ...
+    def server(self, parsed_args): ...
+
+class GatewayYo:
+    gateway: Any
+    def __init__(self, gateway) -> None: ...
+    def server(self, parsed_args): ...
+
+def parse_wsgi_bind_location(bind_addr_string: str): ...
+def parse_wsgi_bind_addr(bind_addr_string: str): ...
+def main() -> None: ...