Refactor the library

Threads are a bad idea because for now the filter API is not guaranteed
to be state-less. The interface is now synchronous, which should be
enough for most filters.
The refactoring brought other changes, the most important being the
concept of modular input sources and output destination and the complete
rewrite of the procedural macro.

opensmtpd/examples/dummy.rs

@@ -1,19 +0,0 @@
-use log::{debug, info, Level};
-use opensmtpd::{event, handlers, Entry, SmtpIn, SmtpdLogger};
-
-#[event(Any)]
-fn on_event(entry: &Entry) {
-    debug!("Event received: {:?}", entry);
-}
-
-#[event(LinkConnect)]
-fn on_connect(entry: &Entry) {
-    info!("New client on session {:x}.", entry.get_session_id());
-}
-
-fn main() {
-    let _ = SmtpdLogger::new().set_level(Level::Debug).init();
-    SmtpIn::new()
-        .event_handlers(handlers!(on_event, on_connect))
-        .run();
-}

opensmtpd/examples/echo.rs

@@ -0,0 +1,18 @@
+use opensmtpd::entry::Entry;
+use opensmtpd::{report, simple_filter};
+
+#[report(v1, smtp_in, match(all))]
+fn echo_handler(entry: &Entry) -> Result<(), String> {
+    log::info!("TEST ENTRY: {:?}", entry);
+    Ok(())
+}
+
+#[report(v1, smtp_in, match(link_disconnect))]
+fn test(entry: &Entry) {
+    log::info!("HAZ LINK DISCONNECT: {:?}", entry);
+    Ok(()) // TODO: REMOVE ME!
+}
+
+fn main() {
+    simple_filter!(echo_handler, test);
+}

opensmtpd/examples/session_event_counter.rs

@@ -1,5 +1,4 @@
-use log::{info, Level};
-use opensmtpd::{handlers, report, Entry, SmtpIn, SmtpdLogger};
+use opensmtpd::{report, simple_filter};
 
 #[derive(Clone, Default)]
 struct MyContext {
@@ -13,6 +12,5 @@ fn on_report(ctx: &mut MyContext, entry: &Entry) {
 }
 
 fn main() {
-    let _ = SmtpdLogger::new().set_level(Level::Debug).init();
-    SmtpIn::new().event_handlers(handlers!(on_report)).run();
+    simple_filter!(vec![on_report]);
 }