windows installer

[Phillip Lord]

I've had a quick play and created an "installer" version of Emacs for
windows. Cheesy and ugly at the moment, but it works. It uses the NSIS
toolkit which is nicely packaged for msys2.

NSIS is free software, albeit the non GPL compatible CPL
(http://nsis.sourceforge.net/License). I don't believe this is a problem
as it would only be a packager. I'd welcome more informed opinion about
whether this is appropriate for Emacs.

Probably too late to put this onto Emacs-26 now I fear, but it could be
ready in time for Emacs-27. If any one is interested, I can uploaded it
to the pre-test website (as the Emacs source is already there).

As with the new zips I've created, this does raise questions about
release of updates to the binaries. This installer will contain (lots
of) other dependency files. My current plan is to freeze the
dependencies during pre-test. But this means, that these dependencies
will get old during the Emacs release cycle.

Anyway, thought's welcome.

Phil