Add Project.toml (#438)

This patch adds `Project.toml` generated by Pkg.jl's `gen_project.jl` script
and removes `REQUIRE` file.

Author: tkf

Project.toml

@@ -0,0 +1,14 @@
+name = "PyPlot"
+uuid = "d330b81b-6aea-500a-939a-2ce795aea3ee"
+
+[deps]
+Colors = "5ae59095-9a9b-59fe-a467-6f913c188581"
+LaTeXStrings = "b964fa9f-0449-5b57-a5c2-d3ea65f4040f"
+PyCall = "438e738f-606a-5dbb-bf0a-cddfbfd45ab0"
+Sockets = "6462fe0b-24de-5631-8697-dd941f90decc"
+Test = "8dfed614-e22c-5e08-85e1-65c5234f0b40"
+VersionParsing = "81def892-9a0e-5fdd-b105-ffc91e053289"
+
+[compat]
+PyCall = "≥ 1.90.0"
+julia = "≥ 0.7.0"