add cg ls, prepare for rc subcommands

src/human.rs

@@ -0,0 +1,35 @@
+use human_units::FormatSize;
+use std::fmt::{Display, Formatter, Result};
+
+pub trait Human {
+    fn human(&self) -> String;
+}
+
+pub struct Quantity(u64);
+
+impl Display for Quantity {
+    fn fmt(&self, f: &mut Formatter<'_>) -> Result {
+        self.0.format_size().fmt(f)
+    }
+}
+
+impl Human for Quantity {
+    fn human(&self) -> String {
+        self.to_string()
+    }
+}
+
+impl Human for u64 {
+    fn human(&self) -> String {
+        self.format_size().to_string()
+    }
+}
+
+impl<T: Human> Human for Option<T> {
+    fn human(&self) -> String {
+        match self {
+            Some(h) => h.human(),
+            None => "◌".to_string(),
+        }
+    }
+}