Adding url crate support

[tonymushah]

this will add the URL crate support for specta
ref : #83
I just added an
#[cfg(feature = "url")] impl_as!( url::Url as String );
in src\type\impls.rs

i'm not sure if it work on export tougth

[Brendonovich]

We probably should have supported url from the start 😅

[tonymushah]

We probably should have supported url from the start 😅

Yes, url is already supported by specta

More details there

[Brendonovich]

I wouldn't call #[specta(type = String)] 'support' for url, more just a workaround. This is much better!