Migrate Data.dcf to a .toml format

[Andrew0Hill]

I think moving Data.dcf to a TOML format makes sense, as this is more versatile than DCF format.

[Andrew0Hill]

It looks like there is an existing R package to read/write TOML: https://www.rdocumentation.org/packages/toml/versions/1.0.0/topics/toml

[Andrew0Hill]

Closing this, I think we should stick with DCF since read.dcf is a base R function, and adding support for some other file format would add a dependency.