made NumericValue.value immutable
made NumericValue.value immutable

alex-vasenin/SwiftAA,alex-vasenin/SwiftAA,onekiloparsec/SwiftAA,onekiloparsec/SwiftAA,onekiloparsec/SwiftAA,onekiloparsec/SwiftAA,alex-vasenin/SwiftAA,alex-vasenin/SwiftAA,alex-vasenin/SwiftAA,onekiloparsec/SwiftAA