Fetch Hex with wget or curl

This way we can use https and do peer verification without bundling
certificates with elixir.
Add file exists check on windows when installing archive
Merge pull request #2756 from elixir-lang/emj-archive-shell

Fetch Hex with wget or curl
Bump Hex requirement
Raise if status code != 0 and use non-verbose modes
Return the proper exit code from powershell