Make Alignment types empty

[V0ldek]

Is your feature request related to a problem? Please describe.
Types implementing Alignment exist only on the type level and never have any reason to be instantiated. It'd be nice if they were impossible to instantiate.

Describe the solution you'd like
Rust gives us a way of doing this – enums with no variants.

enum TwoTo<const N: usize> { }

The above type can never be instantiated. The definitions of all alignment types in the library should be changed to that.