Implements Longstaff-Schwartz algorithm for valuation of American Basket option.

The calling sequence is:

AmericanBasket(payoff,K,S,shares,SamSize,NumInt,
	maturity,covar,interestRate,divDates,divAmounts,...)

EuropeanBasket(payoff,K,S,shares,SamSize,
	maturity,covar,interestRate,divDates,divAmounts,...)
	
Where:

payoff(K,M,Shares,...) is the payoff function; 
	K is the strike price, 
	M is the vactor of assets prices, 
	Shares is the vector containing the number of shares of each stock,
	... additional parameters to be passed to payoff function
	
K - strike price
S - current stocks prices (vector)
Shares - the number of shares of each stock
SamSize - the number of different paths for Monte Carlo
NumInt - number of time intervals into which the time to maturity is to be divided (>=2)
maturity - time to maturity (in years)
covar - the covariance matrix for the stocks (yearly covariance)
interestRate - the yearly interest rate (continuously compound); 0.08 is 8%
divDates - dates when dividends are paid
divAmounts - dividend paid per share

Notes:
divDates and divAmounts are lists, each containing k elements, 
	where k is the number of stocks. For each 1 <= j <= N, divDates[[j]] is a vector 
	containing the dates where dividends for stock j are expected (number of years 
	since now);
divAmounts is a similar list where divAmounts[[j]] is a vector containing dividends which
	will be paid per share of stock j
	
Finally, there is no NumInt for European option.