Higher level client/server API

[wez]

Convenient functions that allow configuring a client or server socket to:

• Buffer send chunks by block and/or line (queue up the writes, they happen async, reads can continue independently unless you request that the write buffer be sync'd up to a certain point)
• Initiate a read of a fixed buffer size. Trigger a callback when the complete read is satisfied or if an error occurred. Set a time constraint on the read.
• Initiate a read of a variable size record and specified terminator. For example, CRLF and LF are two common terminators. Trigger a callback when a complete record is read or if an error occurred. Set a time constraint on the read.

It is desirable for these read functions to return slices over the underlying buffers to reduce copying.

For clients, add an API that allows a new client to be created:

• Specify the target sockaddr to which we want to connect
• If the target is specified textually, handle name resolution using the job API to run eg: getaddrinfo in a thread pool
• client connection happens async; trigger a callback when it completes or fails, or fails to complete with a desired timeout. Provide simple access to the underlying failure reason.

The callbacks mentioned here should be able to be dispatched in a thread pool (or the active scheduler thread) as configured by code for that particular client/server/callback.