support nullable ints and dedicated string dtype
support nullable ints and dedicated string dtype

support for new dtypes
https://pandas.pydata.org/pandas-docs/version/0.25/whatsnew/v0.24.0.html#optional-integer-na-support

https://pandas.pydata.org/pandas-docs/version/1.0.0/whatsnew/v1.0.0.html#dedicated-string-data-type

altair-viz/altair,jakevdp/altair