Add basic models

Signed-off-by: Lee Smet <lee.smet@hotmail.com>

src/time.rs

@@ -0,0 +1,14 @@
+use std::time::{SystemTime, UNIX_EPOCH};
+
+/// A timestamp since the unix epoch
+pub type Timestamp = i64;
+
+/// Get the current system timestamp
+pub fn current_timestamp() -> Timestamp {
+    let now = SystemTime::now();
+    // A duration is always positive so this returns an unsigned integer, while a timestamp can
+    // predate the unix epoch so we must cast to a signed integer.
+    now.duration_since(UNIX_EPOCH)
+        .expect("Time moves forward")
+        .as_secs() as i64
+}