Merge pull request #7 from PerfectMemory/upmaster

Support for localized properties
Update homepage link in gemspec to http://ruby-rdf.github.io/spira/, generated from the README.
raise NoRepositoryError when repository is not set
Merge pull request #14 from cordawyn/cordawyn-fixing-save-errors

raise NoRepositoryError when repository is not set
(the only failing spec is not related to this commit)
using #simple? instead of #plain? for literals without language
Merge pull request #17 from ruby-rdf/localized-attribute-bug

Using #simple? instead of #plain? for literals without language