fixing release

last release (i.e. 0.1.18) was broken and yanked from pypi. this one should have all the latest changes currently on master.

Added flatten_preserve_lists and bug fixes

• Added flatten_preserve_lists, thanks @kaiaeberli
• Fixed unflatten for dataframe with duplicate columns, thanks @kaiaeberli
• Addressed corner cases and squashed bugs, thanks @Outfenneced @mattbornski @andreyz4k @arutledge-xactly

utf8 and bug fixes

• A bug fixed with unflatten_list
• utf8

Unflatten added

• flatten_json can now be referenced as flatten
• Added unflatten function for reversing flatten
• Added unflatten_list for reversing flatten when lists are present

Python 3 support

• Added separator
• A bit cleaner code