core: define initial stream API

Signed-off-by: Marc-Antoine Perennou <Marc-Antoine@Perennou.com>
tests: add test-stream

Signed-off-by: Marc-Antoine Perennou <Marc-Antoine@Perennou.com>
core: add stream struct definition

Signed-off-by: Marc-Antoine Perennou <Marc-Antoine@Perennou.com>
core: implement stream

Signed-off-by: Marc-Antoine Perennou <Marc-Antoine@Perennou.com>