Common time coercion methods
Coerce given value to Date
@example
coercer[Time].to_date(time) # => Date object
@param [Time,DateTime] value
@return [Date]
@api public
Coerce given value to DateTime
coercer[Time].to_datetime(time) # => DateTime object
@param [Date,Time] value
@return [DateTime]
Coerce given value to String
coercer[Time].to_string(time) # => "Wed Jul 20 10:30:41 -0700 2011"
@param [Date,Time,DateTime] value
@return [String]
Coerce given value to Time
coercer[DateTime].to_time(datetime) # => Time object
@param [Date,DateTime] value
@return [Time]
[Validate]