* Added example notebooks + pytest for these notebooks1
* Fixed paths
* Fixing link in docs
* Minor update for pandas 0.25.3
* Updates for pandas 0.25.3
* Fixing doc links with pandas 0.25.3 update.
* Reverting overwrite to changes to notebooks.
* adds support for series.value_counts
* adds docs for series.value_counts
* adds tests for series.value_counts
* updates keyerror language
* adds es docs as an external source
* adds parameters for metrics and terms aggs
* adds 2 tests to check for exceptions
* explains the size parameter
* removes print statements from tests
* checks that es_size is a positive integer
* implements assert_series_equal