Added lookahead(n) method which will peek the symbol n positions beyond the read position. The idea is to use this method to access the read position.
Revised peekNextSymbol() to return lookahead(1), which should always be the same value as what peekNextSymbol() would return
Revised peekNextSymbol() to return lookahead(1), which should always be the same value as what peekNextSymbol() would return