talloc README: more human readible api reference
vf: add three new functions for sending vfctrls down the filter chain

vf_command_all: send command to all filters
vf_command_by_name: send command to named filter
vf_control_by_label: send command to a filter with given label
vf: auto-label video filters if no label is specified.
vf_lavfi: fix ffmpeg deprecation warning for avfilter_graph_parse

use avfilter_graph_parse_ptr for ffmpeg
vf-metadata: copy AVFrame metadata into vf_lavfi priv

store it as mp_tas and add VFCTRL_GET_METADATA to access it from elsewhere
vf-metadata: add vf-metadata property

This is a read-only property that uses VFCTRL_GET_METADATA
to retrieve mp_tags metadata from a filter specified by label
vf-metadata: lua cropdetect example script
vf-metadata: test script
af_lavfi: fix graph parse deprecation warning
af_volume: fix clang -Wsometimes-uninitialized