Add tests from vibe-d:core.

tests/args.d

@@ -0,0 +1,27 @@
+/+ dub.json:
+{
+    "name": "tests",
+    "description": "Command-line argument test",
+    "dependencies": {
+        "vibe-core": {"path": "../"}
+    }
+}
++/
+module test;
+
+import vibe.core.args;
+import vibe.core.log;
+
+import std.stdio;
+
+shared static this()
+{
+	string argtest;
+	readOption("argtest", &argtest, "Test argument");
+	writeln("argtest=", argtest);
+}
+
+void main()
+{
+	finalizeCommandLineOptions();
+}