implement HttpTransport

i took a first stab at #6, doc-blocks and especially tests are yet missing but will be completed - i'd be first interested in some feedback from @bzikarsky? :) 

Is that - at least a bit - like you'd thought it should? `HttpTransport` is mainly based on `UdpTransport`.. i'm open to suggestions, if we should make it more flexible at certain points?
We need a StreamSocketClientTcpTest (like the UDP one) before using the StreamSocketClient for TCP :-)