lballabio/QuantLib-SWIG: 1.22

Main changes for QuantLib-SWIG 1.22 More details on the changes are available in ChangeLog.txt and at https://github.com/lballabio/QuantLib-SWIG/milestone/15?closed=1. As previously announced, this release drops support for Python 2.7, which reached end of life in January 2020. Exported revised SubPeriodCoupon class (thanks to Marcin Rybacki). Exported new FdBlackScholesShoutEngine class. Exported optional discount curve in AnalyticEuropeanEngine constructor. Exported the CrossCurrencyBasisSwapRateHelper (thanks to Marcin Rybacki). Exported new constructors for Asian options (thanks to Jack Gillett). Exported new method hasHistoricalFixing for indexes (thanks to Ralf Konrad). Exported revised OvernightIndexFuture interface. Classes CallabilityPrice, FDBermudanEngine, FDEuropeanEngine, FDAmericanEngine, FDDividendEuropeanEngine and FDDividendAmericanEngine were removed in the C++ library after a deprecation period