combinLibrary   "combin" 
 Description: 
The combin function is a the combination function 
as it calculates the number of possible combinations for two given numbers.
This function takes two arguments: the number and the number_chosen. 
For example, if the number is 5 and the number chosen is 1, 
there are 5 combinations, giving 5 as a result.
 Reference: 
 ideone.com 
 support.microsoft.com 
 combin(n, kin) 
  Returns the number of combinations for a given number of items. Use to determine the total possible number of groups for a given number of items.
  Parameters:
     n : int, The number of items.
     kin : int, The number of items in each combination.
  Returns: int.
