Degu 0.9

For full details on the changes, please see:
  http://docs.novacut.com/degu/changelog.html#september-2014

Security fixes:

  * read_preamble() and read_chunk() now carefully restrict what bytes are permitted, and in particular prevent NUL bytes from being included in any decoded `str` objects

  * Server now limits itself to 100 connections (100 threads); this is hard-coded in 0.9, but will be configurable in 1.0

Breaking API changes:

  * The RGI request signature is now app(session, request, bodies), and wrapper classes like session['rgi.Body'] have moved to bodies.Body, etc.

    For example, this Degu 0.8 RGI application:

    def my_file_app(session, request):
        myfile = open('/my/file', 'rb')
        body = session['rgi.Body'](myfile, 42)
        return (200, 'OK', {}, body)

    Is implemented like this in Degu 0.9:

    def my_file_app(session, request, bodies):
        myfile = open('/my/file', 'rb')
        body = bodies.Body(myfile, 42)
        return (200, 'OK', {}, body)

 * The following four items have been dropped from the RGI session argument:

    session['rgi.version'] # eg, (0, 1)
    session['scheme'] # eg, 'https'
    session['protocol'] # eg, 'HTTP/1.1'
    session['server'] # eg, ('0.0.0.0', 12345)

Performance improvements:

  * The C implementation of read_preamble() is now around 42% faster; this speed-up is thanks to decoding and case-folding the header keys in a single pass rather than using str.casefold(), plus thanks to calling rfile.readline() using PyObject_Call() with pre-built argument tuples instead of PyObject_CallFunctionObjArgs() with pre-built int objects