Removes numerous warnings in v0.4

updated syntax for v0.4 and added Compat as requirement 
Additional PRs have been submitted in Compose, Hexagons, and Loess that were causing the warnings to come up and cause errors with Travis build.

date_bar.jl is commented out in runtests.jl due to InexactError()
Source of the issue is span = (maximum(dates) - minimum(dates)) / (length(Set(dates)) - 1) and subsequent span / 2.
Day cannot support floats which is throwing the InexactError
I originally thought they were related but I went through a did a bunch of manual tests on what is going on here and #502 doesn't fix it. It has to do with trying to make Float type Days (which aren't possible).

Just merged myself and tried testing though anyway... and no luck