implements scalable server push via HTTP multipart/x-mixed-replace for
local or remote messaging, and a minimal (optional) webserver.

what's here:

msgbus
        single-process HTTP/HTTPS message bus / webserver scaling to
        thousands of persistent connections at hundreds of messages
        per second. supports both HTTP/1.0 and HTTP/1.1.

libevmsg
        evented client publish/subscribe API. requires libevent.

msgsend, msgdump
        trivial Python demo clients

chatdemo
        simple interactive AJAX + COMET webchat demo - e.g.
        ./msgbus -d chatdemo and browse to http://localhost:8888/

test-pub, test-sub
        test publisher can flood messages to thousands of parallel
        connections by the test subscriber, or watch the messages at
        http://localhost:8888/msgbus/flood

quick protocol details:

to publish JPEGs as messages on the 'foo' channel:

    POST /msgbus/foo HTTP/1.0
    Content-Type: image/jpeg
    Content-Length: 342
    ...

to subscribe to all messages the 'foo' channel:

    GET /msgbus/foo HTTP/1.0

matching messages are returned in server-push mode, e.g.

    HTTP/1.0 200 OK
    Content-Type: multipart/x-mixed-replace;boundary=XXX

    --XXX
    Content-Type: image/jpeg
    Content-Length: 320
    ...
    --XXX
    Content-Type: text/html
    Content-Length: 53
    ...

or for HTTP/1.1:

    HTTP/1.1 200 OK
    Content-Type: multipart/x-mixed-replace;boundary=XXX
    Transfer-Encoding: chunked

    da
    --XXX
    Content-Type: image/jpeg
    ...
    2b
    -XXX
    Content-Type: application/x-whatever
    ...

to subscribe to only text and image messages on the 'foo' channel:

    GET /msgbus/foo?type=text/*,image/* HTTP/1.1

to subscribe to all messages:

    GET /msgbus/ HTTP/1.0

    HTTP/1.0 200 OK
    Content-Type: multipart/x-mixed-replace;boundary=XXX
    Transfer-Encoding: chunked

    --XXX
    From: dugsong
    Content-Location: /msgbus/foo
    Content-Type: text/plain
    Content-Length: 6
    
    hello
    --XXX
    Content-Location: /msgbus/bar
    Content-Type: application/octet-stream
    Content-Length: 1035
    
    ...