Move library crates under 'lib/'.

Give these crates each a more standard directory layout with sources in
a 'src' sub-sirectory and Cargo.toml in the top lib/foo directory.

Add license and description fields to each.

The build script for the cretonne crate now lives in
'lib/cretonne/build.rs' separating it from the normal library sources
under 'lib/cretonne/src'.

lib/cretonne/src/ir/stackslot.rs

@@ -0,0 +1,45 @@
+//! Stack slots.
+//!
+//! The `StackSlotData` struct keeps track of a single stack slot in a function.
+//!
+
+use std::fmt::{self, Display, Formatter};
+
+/// Contents of a stack slot.
+#[derive(Clone, Debug)]
+pub struct StackSlotData {
+    /// Size of stack slot in bytes.
+    pub size: u32,
+}
+
+impl StackSlotData {
+    /// Create a stack slot with the specified byte size.
+    pub fn new(size: u32) -> StackSlotData {
+        StackSlotData { size: size }
+    }
+}
+
+impl Display for StackSlotData {
+    fn fmt(&self, fmt: &mut Formatter) -> fmt::Result {
+        write!(fmt, "stack_slot {}", self.size)
+    }
+}
+
+#[cfg(test)]
+mod tests {
+    use ir::Function;
+    use super::StackSlotData;
+
+    #[test]
+    fn stack_slot() {
+        let mut func = Function::new();
+
+        let ss0 = func.stack_slots.push(StackSlotData::new(4));
+        let ss1 = func.stack_slots.push(StackSlotData::new(8));
+        assert_eq!(ss0.to_string(), "ss0");
+        assert_eq!(ss1.to_string(), "ss1");
+
+        assert_eq!(func.stack_slots[ss0].size, 4);
+        assert_eq!(func.stack_slots[ss1].size, 8);
+    }
+}