WIP: exploratory branch for fast array views

The code gen for the core indexing computations – both multidimensional and linear – in https://github.com/JuliaLang/julia/commit/c980bae725490aab3f7560dda938235ff9ccb8ad makes me hopeful that we can get array views to be a very fast core component of the language. This approach is really making me wonder if we shouldn't have a simple single-dimensional `Vec` or `Buffer` type that underlies all arrays, in terms of which they can be defined. We could even hide it from sight for the most part, but it makes defining arrays in Julia much more doable.