Added documentation for +beginning_of_hour+ and +end_of_hour+ to Active...

Added documentation for +beginning_of_hour+ and +end_of_hour+ to Active Support Core Extensions guide.

guides/source/active_support_core_extensions.textile

@@ -3064,6 +3064,28 @@ date.end_of_day # => Sun Jun 06 23:59:59 +0200 2010
 
 +beginning_of_day+ is aliased to +at_beginning_of_day+, +midnight+, +at_midnight+.
 
+h6. +beginning_of_hour+, +end_of_hour+
+
+The method +beginning_of_hour+ returns a timestamp at the beginning of the hour (hh:00:00):
+
+<ruby>
+date = DateTime.new(2010, 6, 7, 19, 55, 25)
+date.beginning_of_hour # => Mon Jun 07 19:00:00 +0200 2010
+</ruby>
+
+The method +end_of_hour+ returns a timestamp at the end of the hour (hh:59:59):
+
+<ruby>
+date = DateTime.new(2010, 6, 7, 19, 55, 25)
+date.end_of_hour # => Mon Jun 07 19:59:59 +0200 2010
+</ruby>
+
++beginning_of_hour+ is aliased to +at_beginning_of_hour+.
+
+INFO: +beginning_of_hour+ and +end_of_hour+ are implemented for +Time+ and +DateTime+ but *not* +Date+ as it does not make sense to request the beginning or end of an hour on a +Date+ instance.
+
+NOTE: All the following methods are defined in +active_support/core_ext/date/calculations.rb+.
+
 h6. +ago+, +since+
 
 The method +ago+ receives a number of seconds as argument and returns a timestamp those many seconds ago from midnight:
@@ -3131,6 +3153,13 @@ since (in)
 
 On the other hand, +advance+ and +change+ are also defined and support more options, they are documented below.
 
+The following methods are only implemented in +active_support/core_ext/date_time/calculations.rb+ as they only make sense when used with a +DateTime+ instance:
+
+<ruby>
+beginning_of_hour (at_beginning_of_hour)
+end_of_hour
+</ruby>
+
 h5. Named Datetimes
 
 h6. +DateTime.current+
@@ -3273,6 +3302,8 @@ ago
 since (in)
 beginning_of_day (midnight, at_midnight, at_beginning_of_day)
 end_of_day
+beginning_of_hour (at_beginning_of_hour)
+end_of_hour
 beginning_of_week (at_beginning_of_week)
 end_of_week (at_end_of_week)
 monday