Added more unicode sub/superscripts to Latex tab completions
simplify type unions after instantiation

ref #7017

before it was possible for Union(Vector{T},Vector{Float64}) to end up as
Union(Vector{Float64},Vector{Float64}) after substituting T.
Merge pull request #7018 from lstagner/sub_super

Added more unicode sub/superscripts to Latex tab completions
Pairwise BLAS-based sumabs and sumabs2