BUG: DeltaInSeconds pricesion issue - does not use fractional seconds

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extra : rebase_source : 64a2b14e68d41028a1ce8497303e85865ac1145f
BUG: method should not return reference to local variable
BandMathX : context saving and constant/expression definitions by txt file

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extra : rebase_source : 54a7c69d3e73ab247fc8c5d3eb54c495249abbca
BandMathX app: long description added (but still to be improved)

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extra : rebase_source : bf67af88ac19d26e5eaad0d6cd2db250197fc711
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