Add peg (#4530)

* Add peg

* Force use of PREFIX

* use suggested sed command

packages/peg.rb

+# Adapted from Arch Linux peg PKGBUILD at:
+# https://github.com/archlinux/svntogit-community/raw/packages/peg/trunk/PKGBUILD
+
+require 'package'
+
+class Peg < Package
+  description 'recursive-descent parser generators for C'
+  version '0.1.18-2'
+  source_url 'http://piumarta.com/software/peg/peg-0.1.18.tar.gz'
+  source_sha256 '20193bdd673fc7487a38937e297fff08aa73751b633a086ac28c3b34890f9084'
+
+  def self.build
+    system "sed -i 's,PREFIX = /usr/local,PREFIX = #{CREW_PREFIX},g' Makefile"
+    system "make"
+  end
+  def self.install
+    system "make ROOT=#{CREW_DEST_DIR} install"
+  end
+end