Implement most of the sum domain.
Implement remaining operations on sum and fix broken ones.
Add an example for the sum domain.
Remove domain tranformer by the sum of abstract domains.
Modularize implementation of SumDomain.
Now there is SumDomain which is an abstract class for all sum domains,
SumGenericDomain which is a generic implementations of SumDomain without
heuristics, and SumIntParallelotopeDomain which is for Int+Ptopes with
corresponding heuristics.
Remove print statements from SumDomain.
Modify sum.R to be equal to the main example of the sum paper.
Implements the sum domain combinator.

Merge branch 'sum'