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/isa/encoding.rs

@@ -0,0 +1,78 @@
+//! The `Encoding` struct.
+
+use std::fmt;
+
+/// Bits needed to encode an instruction as binary machine code.
+///
+/// The encoding consists of two parts, both specific to the target ISA: An encoding *recipe*, and
+/// encoding *bits*. The recipe determines the native instruction format and the mapping of
+/// operands to encoded bits. The encoding bits provide additional information to the recipe,
+/// typically parts of the opcode.
+#[derive(Clone, Copy, Debug, PartialEq, Eq)]
+pub struct Encoding {
+    recipe: u16,
+    bits: u16,
+}
+
+impl Encoding {
+    /// Create a new `Encoding` containing `(recipe, bits)`.
+    pub fn new(recipe: u16, bits: u16) -> Encoding {
+        Encoding {
+            recipe: recipe,
+            bits: bits,
+        }
+    }
+
+    /// Get the recipe number in this encoding.
+    pub fn recipe(self) -> usize {
+        self.recipe as usize
+    }
+
+    /// Get the recipe-specific encoding bits.
+    pub fn bits(self) -> u16 {
+        self.bits
+    }
+
+    /// Is this a legal encoding, or the default placeholder?
+    pub fn is_legal(self) -> bool {
+        self != Self::default()
+    }
+}
+
+/// The default encoding is the illegal one.
+impl Default for Encoding {
+    fn default() -> Self {
+        Self::new(0xffff, 0xffff)
+    }
+}
+
+/// ISA-independent display of an encoding.
+impl fmt::Display for Encoding {
+    fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
+        if self.is_legal() {
+            write!(f, "{}#{:02x}", self.recipe, self.bits)
+        } else {
+            write!(f, "-")
+        }
+    }
+}
+
+/// Temporary object that holds enough context to properly display an encoding.
+/// This is meant to be created by `TargetIsa::display_enc()`.
+pub struct DisplayEncoding {
+    pub encoding: Encoding,
+    pub recipe_names: &'static [&'static str],
+}
+
+impl fmt::Display for DisplayEncoding {
+    fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
+        if self.encoding.is_legal() {
+            write!(f,
+                   "{}#{:02x}",
+                   self.recipe_names[self.encoding.recipe()],
+                   self.encoding.bits)
+        } else {
+            write!(f, "-")
+        }
+    }
+}