Add pexec package

packages/pexec.rb

+require 'package'
+
+class Pexec < Package
+  description 'The main purpose of the program pexec is to execute the given command or shell script (e.g. parsed by /bin/sh) in parallel on the local host or on remote hosts, while some of the execution parameters, namely the redirected standard input, output or error and environmental variables can be varied.'
+  homepage 'https://www.gnu.org/software/pexec/'
+  version '1.0rc8'
+  source_url 'https://ftp.gnu.org/gnu/pexec/pexec-1.0rc8.tar.gz'
+  source_sha256 'a968e4774eef80b8b1de3c10e6c0ad2ebeeb732b10e438596f110aa6aaf94a64'
+
+  depends_on 'groff'
+  depends_on 'help2man'
+
+  def self.build
+    system './configure'
+    system 'make'
+  end
+
+  def self.install
+    system "make", "DESTDIR=#{CREW_DEST_DIR}", "install"
+  end
+end