Minor refactor to LogParser

An attempt to simplify the code a bit. Need to do
more.
Trying to pick a sane version requirement for raindrops

Given that this is a major dependency change, I'm trying to pick
something appropriately permissive. I think >= 0.5.0 does the
trick.
Bumping version to 0.4.0

Moving to 0.4.x series because there's a significant dependency
change and a minor interactivity change (not an API change, but
a change to how much information gets returned). Making plans for
1.0, which will probably involve a significant refactoring of the
Scaler.