Add buffer flags. The idea is to make it possible to easily check when a
buffer contains control information that we need to parse to update the
port fields.
Make the client create remote nodes and ports and set up proxies for
them.
Make a port base class implementing most of the logic to pass buffers
locally and remotely.
Remove most code from stream.c, it's now in the port.
Make a portsink and portsrc that can write and read to/from any port. We
use these in the server to send and receive data.
Rework format negotiation. The final format is now sent in-line before
the data. The server will select a format on output ports.
Make it possible to pass custom memory to the builder so that it can
construct packets directly into specified memory and avoid allocs.
Remove GError and GSocketControlMessage in the buffer API to make it
possible to use other (rt-safe) API later.
Add a new refresh message to request a keyframe from the pinos server.
pinospay: pass the refresh-request message upstream
pinossink: turn refresh-request messages into events
pinossrc: turn a keyframe event into a refresh-request message
