Add a script for creating sample dogo site.
Changes listed below.

1. seperate site configurations to a single struct, but not in dogo.Site
2. fix a bug: nil mux
3. fix a bug: nil handler test in mux.Handle function
4. add a helper function IsNil() to lily.go
5. add SiteConfigs to Proc.PageData["Site"]
6. add a pager