Add an XorM data type

XorM is a sum type for AnyM monads which have the same data type, rather than being right biased it is biased toward the active monad.

e.g.

```java
XorM<stream,optional,Integer> nums = XorM.stream(1,2,3);
int result = nums.map(i->i*2)
                 .foldLeft(Monoids.intSum);
//12
```