ubDate: Add or subtract time intervals from dates

 This class allows to model the date giving the possibility to carry out operations like:
 to add or subtract  => day, month, year ,hour ,minute, second ,etc
 It's possible to change the language to obtain the days of the week and the months alone for english and spanish at now.
 when he/she wants himself to create an object of the class he/she is passed a chain with the date in a format determined by you.
Ex:
	date = "05/16/2008 15:06:03"
	format = "m/d/Y h:i:s"
 
The possible characters to use in the format are:
Day --- --- 
	d 	Day of the month, 2 digits with leading zeros 01 a 31
	j 	Day of the month without leading zeros 1 to 31 

Month --- --- 
	m 	Numeric representation of a month, with leading zeros 01 through 12 
	n 	Numeric representation of a month, without leading zeros 1 through 12
Year --- --- 
	Y 	A full numeric representation of a year, 4 digits Examples: 1999 or 2003  
	y 	A two digit representation of a year Examples: 99 or 03  
Hour --- --- 
	B 	Swatch Internet time 000 through 999  
	g 	12-hour format of an hour without leading zeros 1 through 12  
	G 	24-hour format of an hour without leading zeros 0 through 23  
	h 	12-hour format of an hour with leading zeros 01 through 12  
	H 	24-hour format of an hour with leading zeros 00 through 23 
Minute --- ---
	i 	Minutes with leading zeros 00 to 59 
Second --- ---
	s 	Seconds, with leading zeros 00 through 59