Rust Interoperability

Roto types map directly to Rust types for interoperability. The inetnum types use the inetnum crate.

Roto type	Rust type
`bool`	`bool`
`u8`	`u8`
`u16`	`u16`
`u32`	`u32`
`u64`	`u64`
`i8`	`i8`
`i16`	`i16`
`i32`	`i32`
`i64`	`i64`
`f32`	`f32`
`f64`	`f64`
`String`	`roto::String`
`List[T]`	`roto::List<T>`
`IpAddr`	`std::net::IpAddr`
`Prefix`	`inetnum::Prefix`
`Asn`	`inetnum::Asn`
`Verdict[A, R]`	`roto::Verdict<A, R>`
`T?`, `Option[T]`	`Option<T>`
other types `T`	`roto::Val<T>`