Add stack package

packages/stack.rb

+require 'package'
+
+class Stack < Package
+  description 'The Haskell Tool Stack - Stack is a cross-platform program for developing Haskell projects. It is aimed at Haskellers both new and experienced.'
+  homepage 'https://docs.haskellstack.org/en/stable/README/'
+  version '1.4.0'
+
+  case ARCH
+  when 'i686'
+    source_url 'https://github.com/commercialhaskell/stack/releases/download/v1.4.0/stack-1.4.0-linux-i386.tar.gz'
+    source_sha256 'aabd307f7dcb585a7821d7b44a73527f0928a76c48711e6968262ee87c86bc14'
+  when 'x86_64'
+    source_url 'https://github.com/commercialhaskell/stack/releases/download/v1.4.0/stack-1.4.0-linux-x86_64.tar.gz'
+    source_sha256 '618a309d763432a2cca654bc29249a77c7de096c693a28b84dd3656470269f5a'
+  end
+
+  def self.install
+    system "mkdir -p #{CREW_DEST_DIR}/usr/local/bin"
+    system "cp stack #{CREW_DEST_DIR}/usr/local/bin"
+  end
+end