Merge pull request #170 from ghost/master

add packages/yasm.rb

packages/yasm.rb

+require 'package'
+class Yasm < Package
+  version '1.3.0'
+  source_url 'http://www.tortall.net/projects/yasm/releases/yasm-1.3.0.tar.gz'
+  source_sha1 'b7574e9f0826bedef975d64d3825f75fbaeef55e'
+
+  def self.build
+    system './configure --prefix=/usr/local'
+    system 'make'
+  end
+
+  def self.install
+    system "DESTDIR=#{CREW_DEST_DIR} make install"
+  end
+end