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/wsgi.pyi

@@ -0,0 +1,42 @@
+from . import server
+from typing import Any
+
+class Server(server.HTTPServer):
+    wsgi_version: Any
+    wsgi_app: Any
+    request_queue_size: Any
+    timeout: Any
+    shutdown_timeout: Any
+    requests: Any
+    def __init__(self, bind_addr, wsgi_app, numthreads: int = ..., server_name: Any | None = ..., max: int = ..., request_queue_size: int = ..., timeout: int = ..., shutdown_timeout: int = ..., accepted_queue_size: int = ..., accepted_queue_timeout: int = ..., peercreds_enabled: bool = ..., peercreds_resolve_enabled: bool = ...) -> None: ...
+    @property
+    def numthreads(self): ...
+    @numthreads.setter
+    def numthreads(self, value) -> None: ...
+
+class Gateway(server.Gateway):
+    started_response: bool
+    env: Any
+    remaining_bytes_out: Any
+    def __init__(self, req) -> None: ...
+    @classmethod
+    def gateway_map(cls): ...
+    def get_environ(self) -> None: ...
+    def respond(self) -> None: ...
+    def start_response(self, status, headers, exc_info: Any | None = ...): ...
+    def write(self, chunk) -> None: ...
+
+class Gateway_10(Gateway):
+    version: Any
+    def get_environ(self): ...
+
+class Gateway_u0(Gateway_10):
+    version: Any
+    def get_environ(self): ...
+
+wsgi_gateways: Any
+
+class PathInfoDispatcher:
+    apps: Any
+    def __init__(self, apps): ...
+    def __call__(self, environ, start_response): ...