Implement track/stream

* Add Streamer class
* Use FactoryGirl for factories
* Add sha256 field to tracks
* Add mime_type field to tracks

spec/lib/streamer_spec.rb

@@ -0,0 +1,19 @@
+require 'spec_helper'
+
+describe Streamer do
+  describe '#each' do
+    let(:stream) { Streamer.new("#{Rails.root}/spec/fixtures/test.mp3") }
+
+    it 'returns file content' do
+      chunks = ''
+      stream.each { |c| chunks << c }
+      chunks.should == File.read("#{Rails.root}/spec/fixtures/test.mp3")
+    end
+
+    it 'returns content in multiple chunks' do
+      count = 0
+      stream.each { count += 1 }
+      count.should be >= 2
+    end
+  end
+end