Package Errors:
- add function to check & cast error interface into golib Error interface
- update CodeError type to simplify management & error creation
- add function to simplify call of Error function from a generic error interface
- remove some useless function from Error interface
All Other Packages:
- apply change of package Errors into all other packages
- Fix function update (use Version function instead of implement into the update function)
- Add func VersionList to list all version id with contents
- Add func VersionAdd to add new version into the policy as default version
- Add func VersionDel to delete one version of the policy
