Godoc comments for public types and fields

[rydrman]

Adding some descriptions to the types and fields exposed in this library would make it a lot more approachable. I am excited to start using it, but even understanding what is provided in the ResolveParams can require a lot of digging and reading code which doesn't need to be the case. I'd be happy to do some of this work but I am afraid that my understanding of the entire library is still limited so I am likely not the best person for the job.