Use Rust as the source of truth / break with the Go SDK

[LegNeato]

Eventually we'll probably want to have Rust as the source of truth rather than generating from Go.

• Rust's type system is more expressive and can be more correct and ergonomic than what we can infer from Go.
• There are not many maintainers of the Go code so we will always lag behind / wait on them.

We would only want to break with the codegen when we have a critical mass of people using this lib and willing to provide event defs directly in Rust. I don't think we are there but wanted to open this so people can tell me when we are 😄 .

[LegNeato]

@calavera what do you think about this? I feel like most bugs these days are because Go's type system is less expressive and/or they have a bug in their defs.

[calavera]

This is probably the best path forward. #50 is a good example of people providing hand written events. I think the only events I miss so far in this crate are DynamoDB events, and we cannot even generate them from the Go structs anyways.