add a formula for nip2, the libvips GUI

nip2 as a homebrew formula

see

	http://www.vips.ecs.soton.ac.uk/index.php?title=Nip2

for background on nip2

see

	libvips/nip2#48

for users asking for this to be available via homebrew

nip2.rb

@@ -0,0 +1,28 @@
+require "formula"
+
+class Nip2 < Formula
+  homepage "http://www.vips.ecs.soton.ac.uk/"
+  url "http://www.vips.ecs.soton.ac.uk/supported/7.42/nip2-7.42.1.tar.gz"
+  sha1 "46e48e003621c5c63a5bf0e126f7ace0c0b54746"
+
+  depends_on "pkg-config" => :build
+  depends_on "gtk+"
+  depends_on "libxml2"
+  depends_on "vips"
+
+  depends_on "fftw" => :recommended
+  depends_on "gsl" => :recommended
+  depends_on "goffice" => :recommended
+  depends_on "libgsf" => :recommended
+
+  def install
+    args = %W[
+      --disable-dependency-tracking
+      --prefix=#{prefix}
+    ]
+
+    system "./configure", *args
+    system "make", "check" if build.with? "check"
+    system "make", "install"
+  end
+end