Buffer messages that are send to a handler that isn't able to accept them at the moment

[scothis]

Sometimes a handler is unable to handle a message. This is common in cases where a remote socket needs to connect before it can handle a message.

A common facility for wrapping handlers in a buffer would be helpful. The buffer can queue messages when the handler is unavailable and release them once the handler becomes available. Semantics for both the size of the buffer and a timeout for messages in the buffer should be configurable.