Output parseable bundle format

[Nemo157]

Come to think of it exporting to some form of output like xml (or something nicer) with all the fields (including full license text) would make it easy to automatically generate any documents required by different companies compliance departments.

— @xd009642 #68 (comment)

Should be trivial to add another bundle variant that just pipes the result through serde to output a handful of popular formats (first CLI idea, cargo lichking bundle --variant serialize:toml if it's possible to easily support a key-value value like that in clap, otherwise I guess something like cargo lichking bundle --variant serialize --format toml).