Build a Debian package

The first version `0.1.0-rc.0` and metadata for `cargo-deb` is now in
`Cargo.toml`. For that, the service file as well as the config file
were moved.

For a improved systemd service file the `User` and `Group` is now set
via variables and the log level is now set to `info`. In the previous
version of the service file the parameter for `ExecStart` was missing
which prevented this file from working.

The dependencies in `Cargo.lock` were updated.

config.yml

@@ -0,0 +1,40 @@
+---
+hooks:
+  hook1:
+    command: /usr/bin/local/script_xy.sh {{ /field2/foo }} asdfasdf
+    signature: X-Gitea-Signature
+    ip_filter:
+      allow:
+        - 127.0.0.1/31
+    secrets:
+      - secret_key_01
+      - secret_key_02
+    filters:
+      match_ref:
+        pointer: /ref
+        regex: refs/heads/master
+  hook2:
+    command: /usr/bin/local/script_xy.sh asdfasdf
+    signature: X-Gitea-Signature
+    ip_filter:
+      deny:
+        - 10.10.10.0/22
+    secrets:
+      - secret_key_01
+      - secret_key_02
+    filters:
+      match_ref:
+        pointer: /ref
+        regex: refs/heads/master
+  hook3:
+    command: /usr/bin/local/script_xyz.sh
+    signature: X-Gitea-Signature
+    secrets:
+      - secret_key03
+    filters:
+      match_ref:
+        pointer: /ref
+        regex: refs/heads/master
+      match_after:
+        pointer: /after
+        regex: f6e5fe4fe37df76629112d55cc210718b6a55e7e