Rename Hessenberg to HessenbergFactorization

[dlfivefifty]

The following is thoroughly confusing:

julia> a = rand(3,3)
3×3 Array{Float64,2}:
 0.490033  0.522445  0.854002
 0.309698  0.557504  0.495107
 0.980559  0.81369   0.961208

julia> LinAlg.Hessenberg(a)|>full
3×3 Array{Float64,2}:
 0.490033  0.522445  0.854002
 0.309698  0.557504  0.495107
 0.980559  0.81369   0.961208

julia> hessfact(a)[:H] # returns a Matrix{Float64}
3×3 Array{Float64,2}:
 0.490033   0.651441  -0.760193
 1.26273    0.539174  -0.807753
 0.0       -0.48917    0.979538

One would expect Hessenberg(a) to work analogously to Symmetric(a).

See also discussion JuliaMath/Polynomials.jl#130 (comment)

[ViralBShah]

I think we are done with name changes for 1.0 and this is consistent with the others. Perhaps it is ok to close?

[andreasnoack]

this is consistent with the others

The problem here is that the factorization and a matrix involved in the factorization share the same name. I don't think that is the case for any other matrix factorization. I think we should just keep this one open even though it probably won't be fixed in 1.0.