support serializing a vector of strings

[aplavin]

Could probably relax it to allow any vectors (eg numbers)?..

[clarkevans]

@aplavin -- thank you for the pull request.

I'm trying to grok the use cases for this, what are upsides and downsides? Anyway, we're going to be building out an IDE based upon FunSQL over at PlutoFunSQL.jl and putting together a roadmap here.

[aplavin]

This PR simply adds supports for vectors, as in Lit(["a", "b", "c"]). It works fine in my experience (would be nice to finally merge it...).

Ideally though, I think all Julia values in literals (FunSQL.Lit(...)) should be converted to SQL parameters/placeholders, so that they use proper serialization from corresponding DB backends.