Currently to be able to store something in State, the data needs to implement the StateData trait. This StateData trait is really just an alias for Any + Send. It would be really nice if implementing this trait would not be needed. Here are some reasons why:

1. Not technically needed. This abstraction is not actually needed. As you can see in this branch, the StateData can be removed and replaced with direct Any + Send without issues. There is thus no technical reason for the existence of this trait.
2. Unnecessary boilerplate. To be able to store a struct in gotham::state::State, you need to either add the StateData proc-macro to the declaration, or manually implement gotham::state::StateData. This is an extra line of code that is not needed.
3. Forces unnecessary wrapper structs. If you want to store a structure from a crate outside of yours in State, you need to wrap it with of a wrapper struct just so you can implement StateData. This adds unnecessary bloat.

I propose that the StateData trait and StateData proc-macro are removed. All methods on State and FromState that currently take a StateData would take any Any + Send instead.

More benefits:

• This would also be one less thing that users need to learn about when starting out with Gotham.
• Removes ~150 LOC from gotham and examples.