Document usage for asynchronous request-response patterns

[whiskeysierra]

Detailed Description

Apart from being useful in tests, switchboard can (and should?) be developed into a production library in order to enable asynchronous request-response patterns.

Context

If an applications needs a synchronous response from an asynchronous API it basically needs to do the following:

1. issue request event (thread 1)
2. block/wait for response event (thread 1)
3. consume response event (thread 2)
4. hand event over (thread 2 > thread 1)

Possible Implementation

Switchboard basically already supports this right now, but it's actually doing some things that don't really apply for this, e.g. message recording.