Add a "not_like" search operator

[pmuller]

I just stumbled upon the need for this operator. Here is my try to implement it.

[jfinkels]

Since the not_in function uses the tilde (~) instead of the NOT function, I prefer that the not_like function use the same. In other words, remove the import of not_ and replace NOT with ~.

[jfinkels]

Can you please squash your three commits on this branch into a single commit? Then I will merge the changes into the master branch.

[jfinkels]

This was merged in 4637c93.