Fix recursivefill! for VectorOfArray{<:StaticArray} - #261

This PR fixes recursivefill! when attempting to fill a VectorOfArray in which the element type is some sort of StaticArray.

Here is a minimal example:

using RecursiveArrayTools
using StaticArrays

A = VectorOfArray([randn(SVector{3, Float64}, i) for i ∈ 1:4])   # A[i] is a Vector{SVector{...}}

B = recursivecopy(A)
recursivefill!(B, zero(eltype(B)))

C = recursivecopy(A)
recursivefill!(C, false)

In the current master, the calls to recursivefill! respectively fail with:

1. ERROR: MethodError: Cannot `convert` an object of type Float64 to an object of type SVector{3, Float64}                                                                                                           

2. ERROR: MethodError: no method matching fill(::Bool, ::Type{Vector{SVector{3, Float64}}})

This is because, in the called recursivefill! variants, it is assumed that B[i] isa eltype(B), which is generally the case for AbstractArrays. This condition is however violated by VectorOfArray (since in this case B[i] is an AbstractVector{eltype(B)}).

This is fixed in this PR by adding specialisations of recursivefill! for AbstractVectorOfArray{<:StaticArray}.