add socket-level config

[jacobkaufmann]

add socket-level configuration to constructor(s)

the config could include the following:

• max UDP packet size
• max connections

[carver]

I don't think we're ever practically changing connection configurations from one connection to another. I'm starting to think maybe everything could be moved to a Socket level config. That seems easier for the caller than managing two separate configs. What do you think?

[carver]

Splitting the Config into two parts seems to push us in the unpleasant direction of #92.

I'm continuing to lean toward fully removing ConnectionConfig and replacing it with a SocketConfig (or StreamConfig?)