added tests for parsing root config

tests/data/root_config_complex.toml

@@ -0,0 +1,21 @@
+mod_location = "mods"
+download_location = "downloads"
+nexus_api_key = "1234"
+
+[games.sse]
+path = "/home/user/games/sse"
+
+[instances.example1]
+path = "example1.toml"
+
+[instances.example2]
+path = "/home/user/example2.toml"
+
+[mods.mod1]
+path = "/home/user/mods/mod1"
+
+[mods."mod2"]
+path = "mod2"
+
+[mods.mod3]
+path = "mods3"