Switch to Project.toml

[ericphanson]

I think this is needed for GraphRecipes to get a new version in the general registry. I put the version at 0.4.1 but I don't actually know if there were no breaking changes since 0.4.0. (Generated by https://github.com/JuliaLang/Pkg.jl/blob/master/bin/gen_project.jl).

[JackDevine]

Thanks for this, I agree that we need this.

Usually files end with an empty line.

There have been breaking changes since 0.4.0. The most breaking that I can think of is #67 where I changed the way that nodes are drawn. Meaning that markershape and markercolor are replaced by nodeshape and nodecolor. I have been a little slack about tagging a release though, sorry.

[ericphanson]

Ok, thanks for the info! I added in the newline and bumped the version. Though I realized maybe I should've just left the version at 0.4.0 so this PR is just transitioning to project.toml and then leave the versioning to you (or other JuliaPlots maintainers).

[JackDevine]

Closing in favour of #80.