Implement Pkg.update hook

If your package contains a `deps/update.jl` file, it will now be executed
on Pkg.update().
Fix #5804 so eigs works on matrices with dimension less than 6
Merge pull request #5808 from malmaud/n5804

Fix #5804 so eigs works on matrices with dimension less than 6
Remove .git directory/repository of juliadoc in make install
Update package listing
Fix UTF8 detection in some circumstances

e.g. on a typical Ubuntu installation setlocale() could return
something like: "LC_CTYPE=en_US.UTF-8;LC_NUMERIC=en_US.UTF-8;..."
etc. Without the patch this is not recognized as UTF8.

This fixes an issue with left/right arrow keys in the REPL if
Unicode characters are present.
Add unique(AbstractArray, dim)

Efficiently finds the unique columns, rows, etc. of an array. The
algorithm first hashes each row, then finds the unique hashes, and
finally checks that the hashes don't collide. It is roughly O(n) in
the number of elements in the matrix.

This is my first time using Cartesian. Without it, this code is
presently about 10% faster for finding unique rows of a matrix, but
the overhead is probably worth it for the generality.
fix spurious test failure on a system that happened to have an executable named 'foo' in the PATH
probably fix #5818
@parallel documentation in stdlib
Merge pull request #5820 from amitmurthy/amitm/atpdoc

`@parallel` documentation in stdlib
unique(AbstractArray, dim): incorporate @timholy's suggestions
add an internal function to replace Main, use it in sysimg.jl

make the Core.Main binding non-constant, so uses of "Main" in general
refer to the *current* Main. Doing "import Main" will give you a
constant reference to the Main at that time.

fixes #5802

related to #1195
Issue #5455 : Added 1-norm, Inf-norm and Frobenius norm for SparseMatrixCSC
$(DESTDIR)$(prefix)/$(private_libdir) is redundant, should be $(DESTDIR)$(private_libdir)

I spent so much time introducing these Makefile variables, and yet I still have no idea how to use them
Update download links for win-extras

OpenSUSE's packaging moves quicker than ours!
Merge pull request #5717 from xhochy/no-.git-juliadoc

Remove .git directory/repository of juliadoc in make install
Revert "Update download links for win-extras"

This reverts commit af0675311655b8903ff5ecf7d12b184dec94766a.
Update download links for win-extras
Re-re-re update Rmath

Stop fighting me, git