Massively rework the time tracker, mainly to support times across midnight

src/args.rs

@@ -0,0 +1,14 @@
+use clap::Parser;
+
+/// A simple program to track time spans and calculate remaining hours to work
+#[derive(Parser, Debug)]
+#[command(author, version, about, long_about = None)]
+pub struct Args {
+    /// How many hours you intend to work (sums with `minutes`)
+    #[arg(long, default_value_t = 8)]
+    pub hours: i64,
+
+    /// How many minutes you intend to work (sums with `hours`)
+    #[arg(long, default_value_t = 0)]
+    pub minutes: i64,
+}