Provide a way to replace

[EmileTrotignon]

I love this library, this really seems like the right way to do regexp.

However, I had a usecase where I needed to do a search-and-replace, and I found no way to do it. I had to ideas to build it, one being a not combinator to capture everything I don't need to replace, but it does not exists. I also did not find a way to get locations from a match, which would allow replacement.

Since it exists in Re, it would probably not be hard to construct.