Introduce $(build_shlibdir)

Abstracts away the fact that Windows wants shared libraries to be in $(bindir) whereas other operating systems prefer their shared libraries and executables separated
General cleanup of .dll installation

Also removal of .SILENT rule
Fix codespeed submission process
Fix isassigned for BitArrays

(and therefore show_delim_array, show_vector, showall, repr,
the show macro etc.)

Fixes #5754
SharedArray: don't splat for getindex/setindex! dimensions 1-5

Yields a ~10x performance increase for 3-dimensional SharedArrays
Better fix for #5754

Split show_delim_array in two, one version specialized for
AbstractArrays which uses linear indexing and checks for undefs,
and a generic one which uses start/next/done.

Also properly implement isassigned for BitArrays.
Fix #5758
fix bug in rehashing typeToTypeId table. ref #5688
Don't ignore dll installation failure
Merge pull request #5727 from JuliaLang/sf/build_shlibdir

Improve dll installation logic
Whoops, wrong HTTP code.  Also, fix old error message