add initial Ledger and capability to open a gnucash file

lib/gnucash/ledger.rb

@@ -0,0 +1,10 @@
+require "zlib"
+require "nokogiri"
+
+module Gnucash
+  class Ledger
+    def initialize(fname)
+      @ng = Nokogiri.XML(Zlib::GzipReader.open(fname).read)
+    end
+  end
+end