add Book#find_account_by_full_name()

spec/gnucash/book_spec.rb

@@ -0,0 +1,24 @@
+module Gnucash
+  describe Book do
+    before(:all) do
+      # just open the test file once
+      @subject = Gnucash.open("spec/books/sample.gnucash")
+    end
+
+    it "records the date of the earliest transaction" do
+      @subject.start_date.should == "2007-01-01"
+    end
+
+    it "records the date of the last transaction" do
+      @subject.end_date.should == "2012-12-28"
+    end
+
+    it "lets you find an account by id" do
+      @subject.find_account_by_id("67e6e7daadc35716eb6152769373e974").name.should == "Savings Account"
+    end
+
+    it "lets you find an account by full name" do
+      @subject.find_account_by_full_name("Assets::Current Assets::Savings Account").id.should == "67e6e7daadc35716eb6152769373e974"
+    end
+  end
+end