NED convertedto use FileContainer objects
irsa, irsa_dust, and sdss refactored to use FileContainer
alfalfa FileContainer refactor
nvas -> FileContainer
ukidss -> filecontainer
fix StringIO/BytesIO issue
Merge pull request #232 from keflavich/nicer_filelist_reprs

FileContainer wrapper around get_readable_fileobjs
added a demo converted from DotAstro for use at AstroPy:Yale:2013