add integer parsing based off https://github.com/nodejs/llparse/pull/32 And Fix Pausing

[Vizonex]

I'm going to add in integer parsing myself based off @arthurschreiber but with Indutny's requested features and nitpicks.
I will need to make a frame parser for http2 for the aiohttp developers soon since were looking into implementing http/2 protocols, however I would like something a little bit faster than python at parsing frames instead of what hyperframe does which is collecting 9 bits and then depacking. This will skip all of that and cut right to the juicy portions without bloating memory.

SEE: nodejs/llparse#32 for more details.

from llparse import LLParse

def main():
    p = LLParse("frame_parser")
    p.property("i32", "length")
    p.property("i32", "stream_id")
    p.property("i8", "type")
    p.property("i8", "flags")

    body_span = p.span(p.code.span("frame_parser__on_body"))

    root = p.uintBE("length", 3)
    ty = p.uintBE("type", 1)
    flags = p.uintBE("flags", 1)
    stream_id = p.uintBE("stream_id", 4)

    root.skipTo(ty)
    ty.skipTo(flags)
    flags.skipTo(stream_id)

    stream_id.skipTo(
        body_span.start(
            p.consume("length").otherwise(
                body_span.end(
                    p.pause(1, "waiting for next frame").otherwise(root)
                )
            )
        )
    )
    
    data = p.build(root)
    with open('frame_parser.c', 'w') as w:
        w.write(data.c)
    with open('frame_parser.h', 'w') as w:
        w.write(data.header)
    

if __name__ == "__main__":
    main()

Here's a dummy example based off RFC 9113 section 4.1