Update documentation for public types/vars/funcs

[jtraglia]

This PR updates the documentation that can be found publicly here:

• https://pkg.go.dev/github.com/crate-crypto/go-proto-danksharding-crypto

This uses the Go doc tricks mentioned here:

• https://pkg.go.dev/github.com/fluhus/godoc-tricks

Additionally:

• Wrap lines to 120 characters (somewhat arbitrary).
• Update some docs to be more clear.
• Remove unused batch serialization functions.