Version 5.0.0a0

• Adding support for msgpack coverters to_msgpack and from_msgpack
• Adding support for comparision of Box to other boxes or dicts via the - sub operator #144 (thanks to Hitz)
• Adding support to | union boxes like will come default in Python 3.9 from PEP 0584
• Adding mypy type checking, black formatting and other checks on commit
• Adding new parameter box_class for cleaner inheritance #148 (thanks to David Aronchick)
• Changing that sub boxes are always created to properly propagate settings and copy objects #150 (thanks to ipcoder)
• Changing that default_box will not raise key errors on pop or del #67 (thanks to Patrock)
• Changing to_csv and from_csv to have same string and filename options as all other transforms
• Changing back to no required external imports
• Changing from putting all details in README.rst to a github wiki at https://github.com/cdgriffith/Box/wiki
• Changing BoxList.box_class to be stored in BoxList.box_options dict as box_class
• Removing support for single level circular references
• Removing readthedocs generation
• Removing overrides for keys, values and items which will return views again