Add support for generic types

[dwb357]

Given:

@Prototype(kind: .form)
struct Wrapper<Data> where Data: SomeProtocol {
    var field: String
}

the following should be generated:

struct WrapperForm<Data> where Data: SomeProtocol {
   @Binding var model: Wrapper<Data>
...
}

With similar changes being applied for .settings and .view.

This doesn't provide complete support for generics as:

@Prototype(kind: .form)
struct Wrapper<Data> where Data: SomeProtocol {
    var field: String
}

will create a reference using DataForm, but that can be partially addressed in another issue. See #4