Retrieved fields return overly large objects

[Seelengrab]

Consider this struct:

@bitfield struct Foo
    a:3
    b:4
    c:12
end

Currently, accessing all three fields returns an UInt, which is larger than necessary. There is room for returning the smallest existing type for each field, capable of holding the number of bits. I.e., accessing a or b would return an UInt8, accessing c an UInt16` etc.

Alternatively (and much harder), there could be room for returning an UInt3/UInt4/UInt12 type. The issue with that is that julia doesn't have this, and I'd rather not complicate downstream dispatch too much by pulling in an external type. For the same reason, dynamically generating these UIntx types and caching them for future declarations is not an option.