Create vala.rb (#1807)

Add vala language

packages/vala.rb

+require 'package'
+
+class Vala < Package
+  description 'Vala is a programming language that aims to bring modern programming language features to GNOME developers.'
+  homepage 'https://wiki.gnome.org/Projects/Vala'
+  version '0.39.7'
+  source_url 'https://download.gnome.org/sources/vala/0.39/vala-0.39.7.tar.xz'
+  source_sha256 'a54ec96125fdb63dbf96a8a3a65df41fdd88a617c1354088b5e10f8f0c89914d'
+
+  depends_on 'flex'
+  depends_on 'graphviz'
+  depends_on 'libxslt'
+  depends_on 'glib'
+  depends_on 'dbus'
+
+  def self.build
+    system "./configure --prefix=#{CREW_PREFIX} --libdir=#{CREW_LIB_PREFIX}"
+    system "make"
+  end
+
+  def self.install
+    system "make", "DESTDIR=#{CREW_DEST_DIR}", "install"
+  end
+end