Auto-derive Hash for generated Rust structs

Currently Thrift structs are turned into Rust struct definitions that do not have an auto-derived Hash. We should auto-derive this trait.

The following behaviors should be checked:

1. Can still derive Hash even if the struct contains a double
2. Can still derive Hash even if the struct contains set<double>
3. Can still derive Hash even if the struct contains map<double, double>

Basically, doubles are represented in the auto-generated code by OrderedFloat instead of f64 since we cannot derive a hash for, or order Rust floats. The resulting code should work even if doubles are contained any where in the structure.