Merge pull request #37 from jbowtie/master

Add Namespace() to Node interface
xmlNode.SetNamespace should treat an empty prefix as the default namespace
In the common case where a parent has the same prefix and href, reuse the existing xmlNs pointer
Allow for explicit namespace declaration when creating documents with DeclareNamespace().
Adjust logic of SetNamespace() to call C.xmlSearchNsByHref instead of explicitly walking the linked list when looking for existing namespaces.
Run go fmt to fix style issues
Add tests for declaring na namespace and for setting a default namespace
Allow setting value of namespaced attributes
Run go fmt over changed files
Merge branch 'namespaces' of github.com:jbowtie/gokogiri into jbowtie-namespaces
Merge remote-tracking branch 'upstream/master'