Rewrite the project

The previous project architecture was far too complicated and hard to
maintain. The new one is much more simple. Although procedural macros
are cools, they are a no-go on Rust-OpenSMTPD.

Reports and filter are implemented (except data-line) but untested.

src/data_structures/address.rs

@@ -0,0 +1,20 @@
+use std::net::SocketAddr;
+use std::path::PathBuf;
+
+#[derive(Debug)]
+pub enum Address {
+    Ip(SocketAddr),
+    UnixSocket(PathBuf),
+}
+
+impl ToString for Address {
+    fn to_string(&self) -> String {
+        match self {
+            Address::Ip(a) => a.to_string(),
+            Address::UnixSocket(a) => match a.clone().into_os_string().into_string() {
+                Ok(s) => s,
+                Err(_) => String::new(),
+            },
+        }
+    }
+}