Added constraint boolean domains module in file cp/BD.oz
For now it supports the following operations:
- BD.is (test whether is a boolvar)
- BD.decl (declares a new boolvar)
- BD.value (the value when the boolvar is assigned)
- BD.one (test whether the boolvar is 1)
- BD.zero (test whether the boolvar is 0)
- BD.none (test whether the boolvar is neither 1 nor 0)