Remove julia.bat, fixes #4861
Add link to Gentoo package to README

Include link to the gentoo-science overlay which has a package that builds Julia from git
Windows: add NSIS installer builder

This commit adds NSIS installer support for Julia on Windows.

The NSIS installer is built uncompressed, compressed by 7-zip,
then combined into a self-extracting archive using the 7zS.sfx
module from the 7-zip extras distribution. (Thanks to Firefox
for this idea).

The default install directory is %LOCALAPPDATA%, but the user
is prompted to choose a directory before installation. After
installation, the install directory is opened in Windows
Explorer.
WINDOWS: replace setjmp/longjmp with their equivalent in Intel syntax per the objdump disassembler
address readdlm default delimiter and boundserror. ref: #5391
Windows: NSIS improvements

* use Modern UI option for familiar look, and checkbox options at end
* checkbox options (default: checked)
    - open install folder
    - create start menu folder w/ shortcut
* use icon on the install page

Note: the most efficient way to hack on the NSIS file is to make a
dummy build folder with a few text files, and run `makensis` directly.
Split dist build cleanup into dist-clean target
add some more sigatomic sections. fixes #5399