Store package names in arrow metadata

[ericphanson]

for more informative unknown schema errors

closes #46

Here I chose to only store this information when the schema was defined in a package (rather than in Main or in a script or something), since it's only in that case we can reliably make a suggestion to load that package.

[ericphanson]

good call @kleinschmidt, I've switched this to use the schema-version instead of the schema name (defined in the @version call rather than the @schema call)

[omus]

@ericphanson you probably also want to include the version of the package as well since older or newer versions may be incompatible.