Switching out curb in favor of Raindrops::Linux listener stats

Using Raindrops' built-in methods to gather the :active and
:queued data. This does mean forfeiting the :calling and :writing
data; those numbers are not actively used by alicorn, but may be
useful to some users for informational purposes. The code
simplification is worthwhile, though, and this allows users to
switch off the Raindrops middleware which was previously required.
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.