Allow interpolating AbstractVector{<:AbstractVector}

[goretkin]

if function (A::LinearInterpolation{<:AbstractVector{<:Number}})(t::Number) were generalized beyond <:Number to perhaps <:AbstractVector then

1. You could support e.g. Vector{SVector}
2. function (A::LinearInterpolation{<:AbstractMatrix{<:Number}})(t::Number) could be written in terms of a reinterpret/reshape and the previous definition. The package would have to come to depend on StaticArrays.jl, as far as I can tell, however.

And so on for the interpolation methods that only require vector space operations on the data.

[baggepinnen]

It would be great to have some way of interpolating vector-valued time series, e.g.,

CubicInterpolation(u, t, dims=1)

if u is a matrix with time in the first dimension. For example like this

u_i   = CubicSpline.(eachslice(u; dims), Ref(t))
τ     = t -> [u(t) for u in u_i]

[baggepinnen]

The Vector{SVector} case works after #78.

[andreasnoack]

Fixed by #78