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've merged #502 . Does that make these tests pass now?