Add restaurant example

+[package]
+name = "restaurant"
+version = "0.1.0"
+authors = ["Georg Hopp <georg@steffers.org>"]
+edition = "2018"
+
+# See more keys and their definitions at https://doc.rust-lang.org/cargo/reference/manifest.html
+
+[dependencies]

+//
+// Restaurant lib for demontrating rust modules.
+//
+// Georg Hopp <georg@steffers.org>
+//
+// Copyright © 2019 Georg Hopp
+//
+// This program is free software: you can redistribute it and/or modify
+// it under the terms of the GNU General Public License as published by
+// the Free Software Foundation, either version 3 of the License, or
+// (at your option) any later version.
+//
+// This program is distributed in the hope that it will be useful,
+// but WITHOUT ANY WARRANTY; without even the implied warranty of
+// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+// GNU General Public License for more details.
+//
+// You should have received a copy of the GNU General Public License
+// along with this program.  If not, see <http://www.gnu.org/licenses/>.
+//
+
+mod front_of_house {
+    mod hosting {
+        fn add_to_waitlist() {}
+        fn seat_at_table() {}
+    }
+
+    mod serving {
+        fn take_order() {}
+        fn serve_order() {}
+        fn take_payment() {}
+    }
+}