This adds a top-level document for the new `to` command, with a list (of links) of all the subcommands.
All the to-* subcommands keep their filename, but the content is updated to use the new subcommand syntax.
Since not all subcommands have documentation, some items in the list are just text without a link. Also filled the list for the undocumented from* commands in the same style.
Fixes#1709
fixes#969, admittedly without a --delimiter alias
moves from_structured_data.rs to from_delimited_data.rs to better
identify its scope and adds to_delimited_data.rs. Now csv and tsv both
use the same code, tsv passes in a fixed '\t' argument where csv passes
in the value of --separator
Partial fix of issue #711
Docs for the following commands were added -
to-csv
to-json
to-toml
to-tsv
to-url
to-yaml
Docs for to-db , to-bson , to-sqlite have not been added as I don't recognize and understand those formats.
