Add help to date_bin and aggregator

Author: mlell

beanquery/query_env.py

@@ -803,12 +803,14 @@ def date_bin_str(stride, source, origin):
     function also accepts strides containing units of months and years.
     
     Arguments:
-      stride: A string representing a time interval, e.g. '1 day', '1 month', '1 year'; source: The date to bin; origin: The start of the binning interval
+      stride: A string representing a time interval, e.g. '1 day', '1 month', '1 year'; Make sure to use single quotes in the first argument, as 
+      double-quoted strings are parsed as column names for backwards compatibility.
+      source: The date to bin; origin: The start of the binning interval.
     """
     return date_bin(interval(stride), source, origin)
 
 
-def aggregator(intypes, name=None, groups=None):
+def aggregator(intypes, name=None):
     """Decorator to register an aggregator function.
     
     Args: