Added `head` parameter to `query` to allow querying the earliest `head` records in each group found.
0.4.2.post1
Added note for contributors.
0.4.2
Explicitly use "UTC now" for relative timestamps.
0.4.1
Addressed Pandas future deprecation warning:
FutureWarning: The parsing of 'now' in pd.to_datetime without `utc=True` is deprecated. In a future version, this will match Timestamp('now') and Timestamp.now()
0.4.0.post1
Updated documentation to include notebook example.