Previously, queryArguments was partially implemented to handle the most
common types I had run into, with a TODO to complete the rest.

This change implements the support for the remaining argument types.
Now, slices of T are mapped to "[T]!", and pointers to slices of T are
mapped to "[T]", as per GraphQL specification.

Add a comment pointing out that commas are omitted because they're
insignificant, and we're looking to produce minified output (less bytes
to send over the network).

Fixes #6.