Handle library/title sorting on backend (#86)

spec/util_spec.cr

@@ -38,6 +38,9 @@ end
 describe "chapter_sort" do
   it "sorts correctly" do
     ary = ["Vol.1 Ch.01", "Vol.1 Ch.02", "Vol.2 Ch. 2.5", "Ch. 3", "Ch.04"]
-    chapter_sort(ary.reverse).should eq ary
+    sorter = ChapterSorter.new ary
+    ary.reverse.sort do |a, b|
+      sorter.compare a, b
+    end.should eq ary
   end
 end