Create map keys functionality

[Adzz]

Would be cool if we could map between structs, specifying which key in the one struct maps to the key in the other struct.

EctoMorph.translate(%MyStruct{field: "yis"}, %YouKnow{}, [field: :other])
# => %YouKnow{other: "yis"}
EctoMorph.translate(%MyStruct{field: "yis"}, %YouKnow{}, [field: :other])

Or something. Probably could do with a better API for it and naming, potentially with map_values function to?

Cast to struct will translate values for us, when the keys match... but would be cool if we can specify a key becoming another key. Need to be carful cast_to_struct doesn't become mental

EctoMorph.cast_and_translate_to_struct(%MyStruct{field: "yis"}, %YouKnow{}, [:field], [field: :other])
# => %YouKnow{other: "yis"}

In fact when you think about it, all the rest falls out of this. Like cast to struct is a translate, where the keys are just equivalent.

EctoMorph.translate(%MyStruct{field: "yis"}, %YouKnow{}, [field: :field], )
# => %YouKnow{field: "yis"}

EctoMorph.cast_to_struct(%MyStruct{field: "yis"}, %YouKnow{}, [:field])
# => %YouKnow{field: "yis"}

Names

It's not really a map, as it doesnt preserve the original struct, is more like a reduce. translate coerce cast cast_with_* cast_to_struct - just have extra options cast_keys