Refactored __str__ for superboxes.  #175
Parsing unknown superboxes with known 1st sub box.  #175
Improved the warning when an exif tag is bad.  #175
Refactored superbox parsing.  #175
Some pylint work.
Added print support for unknown boxes.  #175
Starting write support for ftbl and flst boxes.  #175
FileType box sanity checks.  #175
Allowing DataReferenceBoxes to be empty.  #175
More negative tests.  #175
More negative tests.  Incompatible change to ChannelDefinitionBox.  #175
More negative tests, pylint work.  #175
Added ftbl/data reference test.  Removed bad asoc check.  #175
Verifying that data entry url box URLs are null terminated.  #175
Added proof of concept test for linking exterior codestreams.  Closes #175
Merge branch 'issue175' into devel