[ENHANCEMENT] Decide on default position definitions for eltype and ndims

[mtfishman]

Right now there is a generic definition for any AbstractArray subtype that the first parameter is eltype and the second is ndims, that is of course incorrect for some AbstractArray subtypes but it is a very convenient definition since most AbstractArrays follow that convention.

[mtfishman]

We could make it a bit safer and define position(type::Type{<:AbstractVecOrMat}, ::typeof(ndims)) = error("No position.") which would catch many cases I can think of where the current definition is wrong.

[mtfishman]

We could make it a bit safer and define position(type::Type{<:AbstractVecOrMat}, ::typeof(ndims)) = error("No position.") which would catch many cases I can think of where the current definition is wrong.

Actually never mind, that wouldn't be a good idea since many AbstractVecOrMat are type aliases of an AbstractArray in which case ndims is a type parameter (that happens to be hard-coded to a certain value).