hooks can now interrupt or redirect actions, and initiate
related actions, by printing json on stdout with commands
mainly to mitigate limitations such as sharex/sharex#3992
xbr/xau can redirect uploads to other destinations with `reloc`
and most hooks can initiate indexing or deletion of additional
files by giving a list of vpaths in json-keys `idx` or `del`
there are limitations;
* xbu/xau effects don't apply to ftp, tftp, smb
* xau will intentionally fail if a reloc destination exists
* xau effects do not apply to up2k
also provides more details for hooks:
* xbu/xau: basic-uploader vpath with filename
* xbr/xar: add client ip
