ASGI Support for HTTP

[mliezun]

ASGI Support for HTTP

Fixes #5

• Implemented support for ASGI HTTP events.
• Created new AsgiApp object and created new AsgiApp_* functions in C.
• Renamed previously named App_* functions to WsgiApp_*.
• Created new AsgiEvent python class to store state of an execution of an ASGI app.
• Renamed HTTPHeaders object to MapKeyVal because is used in other places as a more general data structure.
• Pinned Ubuntu to 22.04 instead of latest to fix CI.
• Added requirements.txt to examples.
• Updated Readme with information about ASGI.
• Moved init code to new file caddysnake.py which is embedded by Go using fs.Embed and setups the initial threads for Wsgi and Event pool for Asgi.
• Formatted all python files with black.
• Parsing new module_asgi directive in Caddyfile.
• Created new handler for ASGI requests in Go: AsgiRequestHandler.

TBD

• Websockets support for ASGI.