added api_descriptors and spec/fixtures/external_documents_* directories - generated by spec
support of templated transitions
delete transitions
merging develop
fixing embed spec
templated_url method refactoring
xhtml serializer refactoring
addressing pr comments: begin end block in templated_url method
addressing PR comments
{} instead of do end block for single line method calls
Merge pull request #68 from mdsol/feature/refactoring_xhtmlserializer

refactoring xhtml serializer