Add file storage

spec/storage_spec.cr

@@ -0,0 +1,17 @@
+require "./spec_helper"
+
+module Dayoff::Test
+  describe Storage do
+    it "can store data in file" do
+      with_temp_dir do |tmpdir|
+        storage = FileStorage.new tmpdir
+        storage.set_planned_dates [
+          PlannedDate.new(d(1), 8),
+          PlannedDate.new(d(1), 8),
+        ]
+        entries = Dir.glob(tmpdir + "/*")
+        1.should eq entries.size
+      end
+    end
+  end
+end