Added 'framelimits' attribute that is always added to object.  Other metadata is for entire cine file, while the actual data present is usually a small subset.
Added save_hdf5 method to Cine class.  This makes it simple to save a cine file with all of its metadata to h5.  The structure of the h5 file is such that 'images' is the only data in the root group.  TaggedBlocks is a subgroup containing the data in the tagged blocks, and there is a link in the root group to TaggedBlocks/time_float if it exists.  All other metadata is saved in the attrs dictionary.