These are quite expensive, because they go through all events to index
in a typed array that no longer exists. Clients should index in the
union array and find the event they want themselves, or use dispatch.
Instead of synchronously handling events as they happen in
`tox_iterate`, this first collects all events in a structure and then
lets the client process them. This allows clients to process events in
parallel, since the data structure returned is mostly immutable.
This also makes toxcore compatible with languages that don't (easily)
support callbacks from C into the non-C language.
If we remove the callbacks, this allows us to add fields to the events
without breaking the API.
