Add IsIdentifiableVecOfVia trait and newtype_identified_vec macro

[Sajjon]

Big PR adding powerful features, that allows you to create a new type using the newtype_identified_vec macro.

You use it like so:

newtype_identified_vec!(of: User, named: Users);

It creates this:

#[derive(Debug, Clone, Eq, PartialEq)]
pub struct Users(IdentifiedVecOf<User>)

impl IsIdentifiableVecOfVia<User> for Users { ... }

The trait IsIdentifiableVecOfVia is also new, which inherits from IsIdentifiableVec - also a new trait to where all previous methods (well almost all, except a few... might do them later) and functions are moved - the IsIdentifiableVecOfVia trait allows a type to act as if it is IsIdentifiableVec via a field it has.