feat(realpaver): make c++ code-base
feat(util/interval): add util/interval class
feat(util/scoped_env): use util/interval
feat(realpaver/rp_propagator): use util/interval to print out interval in proof
fix(realpaver/rp_variable): rp_union_display_simple gets "out" param
feat(dsolvers): icp and nra solvers use util/interval