Improve documentation and examples.
Use pathtools for filenames.
Add class MosaicExperiment(Experiment).
Use pathtools for filenames.
Add stageinfo to ImageData class.
MosaicData: add method add_subvol().
MosaicDataCuboid: add method and instance vars for overlap.
Add abstract method add_mosaics().
MosaicExperiment: add supplement dict.
Update docstrings.
Make 'dim' a private variable.