* add support for series plotting
* update docs for series plotting support
* add tests for series plotting
* fix typo
* adds comment to ed_hist_series
* 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