Ben

@mattbierner what are you using to test performance?

I think the problem is with the sizes (relaxed indices?) [here](https://github.com/nicolasstucki/scala-rrb-vector/blob/master/core/src/main/scala/scala/collection/immutable/rrbvector/RRBVector.scala#L2005) since we're prepending we can't reuse the existing cache, and must always rebuild it

Why do we need to address line numbers? Isn't that more 'meta-content' than actual 'content'? For example, I wouldn't expect different colored text to be handled and differently than plain...