Detect when numbers cancel each other out in expression

[jfmengels]

This would be a follow-up to the idea in #41 and the PR done in #122.

The rule currently reports the following:

n - n
--> 0

-n + n
--> 0

but it doesn't catch something like this

something + n + else - n -- notice the 2 n cancel each other out
--> something + else

This would be nice to have, and I think that this will catch more problems than n - n.

Just like n - n, this simplification should not be enabled when we the rule is configured with expectNaN.