Set version to 0.8.0 (#79)

And change over to Project.toml while we're at it.

Author: mortenpi

Project.toml

@@ -0,0 +1,12 @@
+name = "DocStringExtensions"
+uuid = "ffbed154-4ef7-542d-bbb7-c09d3a79fcae"
+version = "0.8.0"
+
+[deps]
+LibGit2 = "76f85450-5226-5b5a-8eaa-529ad045b433"
+Markdown = "d6f4376e-aef5-505a-96c1-9c027394607a"
+Pkg = "44cfe95a-1eb2-52ea-b672-e2afdf69b78f"
+Test = "8dfed614-e22c-5e08-85e1-65c5234f0b40"
+
+[compat]
+julia = "≥ 0.7.0"