Fixed some bugs:

Fixed some bugs:
	- The name in the function Tan(x) is now properly initialized
	- While printing names, the minos in front of the coefficients is now well treated
	- Added equality check for computing the gcd of DDFunctions
	- Added equality check for division computation

Added more examples:
	- Arcsin, Arccos, Arctan
	- The function Arccos create a parameter called 'pi'