discardmeans that the interval and it's children are not participating in the determination of the total integral anymore because it's parent did a refinement when the data of the interval wasn't known, and later it appeared that this interval had to split
completeall the function values of the interval are known
donethe integral and the error for the interval has been calculated
branch_completethe interval can be used to determine the total integral, (but if it's children are also branch_complete, they should be used.)
Closes #5 (closed).