Composer's autoloader support

Added support for Composer's autoloader (the original custom autoloader is still retained and can be used in its stead)

New TimeUtils util class

Added TimeUtils class for converting time lengths

Moved the getResultAsArray method's implementation

The getResultAsArray method's implementation was moved upstream into the CalculatorAbstract abstract class and now accepts an optional argument for subsetting properties (otherwise it takes in the propResultArray class field of the individual calculator class which extends the CalculatorAbstract)
Also added some shorthand methods into the AnnuityCalculator

New StockInvestmentRatiosCalculator

Added calculator for calculating investment ratios of stocks/shares

Streamlined the structure of the calculators' classes

Moved the calculators' getter methods directly into the calculators' classes obviating the need for the "result" objects and thus removing the unnecessary doubling of the constructors

New JSONSerializer

Added a new serializer to JSON format

New result output methods

Added support for serialized output of calculators' results
Added an XML serializer

Streamlined the DebtAmortizator

Removed the unneeded 'DebtPaymentType' property from the DebtAmortizator class – this made the things less confusing and cut the number of its factory methods by half

New BondDurationCalculator

Added calculator for calculating bonds' duration

New BondYTMCalculator

Added calculator for calculating bonds' Yield-to-Maturity