This will allow passing both cli options and format options to sub decoder.
Ex: pass keylog option to a tls decoder when decoding a pcap.
Ex: pass decode options to a format inside a http body inside a pcap.
Add ArgAs method to lookup argument based on type. This also makes the format
decode function have same signature as sub decoders in the decode API.
This change decode.Format a bit:
DecodeFn is now just func(d *D) any
DecodeInArg renamed to DefaultInArg
Preparation to make decoder use less memory and API more type safe.
Now each scalar type has it's own struct type so it can store different
things and enables to have a scalar interface.
Also own types will enable experimenting with decode DLS designs like
using chained methods that are type aware.
Markdown is used as is in online documentation and in cli the markdown decoder
is used to decode and the some jq code massages it into something cli friendly.
Was just too much of a mess to have doc in jq.
