Add inequality comparison operator

[uncenter]

Current behavior:

There is no inequality comparison operator. One must write the more verbose form of not (@foo = 1) whereas @foo != 1 is preferred. This was first suggested in 2012 in #674 but closed as "superfluous", but I think this would make sense to add - programming languages usually don't make you write !(foo === 1) (JavaScript) for example.

[matthew-dean]

This is not a bad idea.