I began on an implementation of the timestamp API described in #363 but
quickly realised that it might be best to land the API for providing
extra information to the user's callback first.
This PR adds two new types: `InputCallbackInfo` and `OutputCallbackInfo`.
These types are delivered to the user's data callback as a new, second
argument.
While these types are currently empty, the intention is for these types
to provide information relevant to the current request for or delivery
of data. This includes:
- Timestamp information #363.
- Flags related to the state of the stream (e.g buffer
underflow/overflow).
In order to maintain flexibility to avoid breaking things, I figure we
can keep the fields of these types private and provide methods for
retrieving this info.
@Ralith, @ishitatsuyuki does this seem OK to you?
bcf962c447