Making listToSceneInterfaceNameList public so we can use it in IECoreMaya bindings
Tidying up the Houdini custom tag code before porting over to Maya
Changed customTagReader registration to match IECoreHoudini.

Custom tag readers now register both has and read functions, and are no longer registered on tag name. They instead allow any dapPath to have or read any tag, and all custom tag readers will be called during readTags.
SceneShape registers a custom tag reader with MayaScene.

This simply translates the tags already existing in the scene file, and does not currently allow for live editing/addition of tags.
adjusting test for python tag registration so it doesn't interfear with the SceneShape test
Merge pull request #20 from andrewkaufman/mayaSceneTags

Maya Custom Scene Tags