Historical VaR made positive, only positive returns scenario added
excute date parameter behaviour corrected
First dates case managed, tests and comments added
Completed comment in VaRHistorical::execute()
Merge pull request #53 from pchaigno/var-historic-patch

Var historic patch
Merge branch 'master' into var-riskmetrics
VaRAlgorithm::checkDate() written
Lambda parameter made constant, Licence text added to MathFunctions.cpp, VaRRiskmetrics::execute() code slipt and commented