v0.0.2

Added

• Support of basic MS Excel logical functions
• Support of most MS Excel web functions
• Support of arithmetic and comparison operators of MS Excel as functions. Use AND(F.GT(1, 3), F.LT(1, 3)) instead of AND(1>3, 1<3)
• There is a new error type for not yet implemented functions, Error::NotImplemented
• There is a new expression variant for null values, Expr::Null