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.