Fix JuliaLang/julia#6665

Provides airyx in addition to bessel[jyikh]x
Tweaks to StepRange: Take 2
Updates following discussion in JuliaLang/julia#6665

Rather than introducing bessel[hijky]x functions, introduce optional
positional argument to bessel[hijky] and airy for scaled version.
deprecate readsfrom/writesto in favor of simply using open on AbstractCmds, and support: open(cmd, mode) do io ... end
better rearrangement of try/catch block in open(f, cmds)
Added more unicode sub/superscripts to Latex tab completions
rm obsolete writesto docs
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.
improve docs for isready(). closes #7006
Merge branch 'master' of github.com:JuliaLang/julia
Merge pull request #7018 from lstagner/sub_super

Added more unicode sub/superscripts to Latex tab completions
fix #6980, method sorting bug
Pairwise BLAS-based sumabs and sumabs2

Also speed up sum/sumabs/sumabs2 for very small vectors
Merge branch 'sjk/pairwise-sumabs2'
automatically NULL-terminate UTF16 data for passing to Windows (and similar) APIs
Tweaks to sum across dimensions

- Implement sum(fn, A, region)
- Implement Base.sumabs across dimensions
- Use pairwise summation/BLAS for sums across first dimension
remove redundant code for AsyncStream readline
use Any[] explicitly for a few things in Base that want it, to make it independent of the behavior of map()
NULL-terminate UTF32String data for consistency; deprecate UTF32String(c::Char...) in favor of utf32(c...); add conversion to UTF32String from binary data that looks at the BOM
NEWS updates for UTF16String and UTF32String