Extracted read_posts from site.rb into reader.rb

- Extracted
  - Updated References
  - Ran Tests

Signed-off-by: Martin Jorn Rogalla <martin@martinrogalla.com>

test/test_site.rb

@@ -189,7 +189,7 @@ class TestSite < JekyllUnitTest
     end
 
     should "read posts" do
-      @site.read_posts('')
+      @site.reader.read_posts('')
       posts = Dir[source_dir('_posts', '**', '*')]
       posts.delete_if { |post| File.directory?(post) && !Post.valid?(post) }
       assert_equal posts.size - @num_invalid_posts, @site.posts.size

test/test_tags.rb

@@ -13,7 +13,7 @@ class TestTags < JekyllUnitTest
     site = Site.new(Jekyll.configuration)
 
     if override['read_posts']
-      site.read_posts('')
+      site.reader.read_posts('')
     end
 
     info = { :filters => [Jekyll::Filters], :registers => { :site => site } }