Have Encoder work with struct values not just pointers

[yonderblue]

This might be more of a question than an issue, but I didn't see it in the docs.

All the examples show giving a reference to .Encode() but the regular encoding/json package supports giving a struct value as well. When I tried I got "ffjson marshal not available for type.." Otherwise loving the library :) Pretty slick when paired with go generate.