Renato Marroquin

Add timediff as another time operationr function

5

closes #41 baed on https://cloud.google.com/bigquery/docs/reference/standard-sql/time_functions#time_diff and https://github.com/ibis-project/ibis-bigquery/pull/40/files#r620526603 I added a `TIME_DIFF` hey @tswast I tried adding a unit test but it is not working :( I am getting the following...