Data from iterables

[0.3.5] (2019-05-14)

Added

• Arche() supports any iterables with item dicts, fixing jsonschema consistency, #83
• Items.from_array to read raw data from iterables, #83

Changed

• If reading from pandas df directly, store raw data in numpy array. See gotchas http://pandas.pydata.org/pandas-docs/stable/user_guide/gotchas.html#support-for-integer-na