Standard interface for loading a concrete IBundleManifest.
Using this the application can make a chain of loaders as long as each layer implements this interface. Augmented by the LoaderExtensions.
|IOperation||Begin (BundleManager manager, string absolutePath, int version, string baseUrl)|
Sets the source URL to the manifest and where all remote content is expected to be found.
Can be updated during application run for a version change.
|version||If cached locally and version number matches, won't hit network|
|absolutePath||manifest path. Not necessarily from baseUrl|
|baseUrl||prepended to all bundle requests. Ends with slash. Typically BundleManager.GetUrlPath(absolutePath).|
Get the current directory
Only valid after Initialize completes without error.