remove pandas dependency in formatting (#217)
remove pandas dependency in formatting (#217)

* Update the datetime and timedelta formatting: no longer pandas dependant.

* Fix NaT issue in dataframe.formatting

maartenbreddels/vaex,maartenbreddels/vaex,maartenbreddels/vaex,maartenbreddels/vaex,maartenbreddels/vaex,maartenbreddels/vaex