width must be a multiple of 2
rename a control command
remove spurious warning
unmap data before releasing the uref
fix comment
add application tutorial
pass references to upump for upipe_input

Also increments the reference count of source pipes when outputting packets.
This fixes an issue with rogue pointers if control commands are sent to the
source pipe from a probe, which change or release the pump.
fix make dist
uprobe_gl_sink_cube: (bi)linear upscale

Use GL_LINEAR magnify filter.
new upipe_*_chain_output* API

This new API also releases the input pipe. It is useful for statically
building pipelines.
fix amend_flow_format in upipe_dup
remove spurious warning
fix ubuf_pic_clear
fix picture alignment
fix deselection of deleted flows
do not output pictures before sequence header
fix multiple corner cases
tutorial part 2
fix wrong refcounting with udp sink
fix sound flow def