Support for lifetimed struct

[NavyaZaveri]

I'm trying to use the ElasticType macro against a struct parameterized on a lifetime, like so:

#[derive(ElasticType, Serialize, Deserialize)]
pub struct Xkcd<'a> {
       link: &'a str
}

This throws an error:

#[derive(ElasticType, Serialize, Deserialize)]
 |       ^^^^^^^^^^^ expected lifetime parameter

As far as I'm aware, Rust doesn't have any semantics for parameterizing macros. If a fix isn't possible, It would be more useful to see an error message stating it's not possible to use ElasticType on a lifetimed struct.