Move this out of the namespace scope.

Change-Id: I4aec1d45edb47ea16adaa8d2ac23340b8f421bae
Remove inline methods from the header.

Change-Id: Ie2cff194c1db5eaa992c4bcaaa06ec9a419d85a7
Move this header out into a public place.

Change-Id: I356b26947d1018276d8a9ff6012fdad3ca2c0fd8
Add a means to check if a namespace exists.

Useful when we just need to check if the stream has a certain namespace
defined. Calling getNamespaceURL() may throw SAXException in such case.

Change-Id: Ib2b7b202492390158270d87bab95d1793c9d8a70