Fix issues in determining return type of sum/prod along dim

- Fix reductions along dimensions of Union typed arrays
- sumabs/sumabs2 for Complex64/Complex128 should return Float32/Float64
fix #7174, mostly
fix #7082
export maxabs and minabs
Document compiler flags for using Intel compilers and libraries.
Slightly updated instructions for icc and mkl.
Revert "Slightly updated instructions for icc and mkl."

This reverts commit 3ba3d1d251213b005f94c87dcac571d2603518b6.
Updated instructions for icc and mkl only, and no other breaking stuff.
fix ref #7082
fix terminal size detection in mintty

use try catch and open from t.out_stream
Merge pull request #7620 from JuliaLang/tk/mintty-size

fix terminal size detection in mintty
fix return type of size(t::TTYTerminal)

for consistency with other platforms
Merge pull request #7539 from JuliaLang/sjk/reducedim_type

Fix issues in determining return type of sum/prod along dim
windows: download links
WINDOWS: fix some other issue mentioned in #7082 where NamedPipes can freeze up
link "fetch" too
Merge pull request #7624 from waldir/patch-1

link "fetch" too
New version of mingw64-libexpat
Merge pull request #7627 from ronisbr/master

New version of mingw64-libexpat
Quick fix to metaprogramming.rst