A OneTouchOption pays a fixed amount of money, called the rebate,
if a previously determined exchange rate ever trades at a previously determined
touch-level until a specified expiry time T.
A OneTouch-option is also sometimes called one-touch-digital or hit option. Furthermore,
this option can be interpreted as an American Cash-or-nothing-digital option, if
the rebate is in domestic currency, or as an American Asset-or-nothing-digital option,
if the rebate is in foreign currency.