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/mod.rs

@@ -0,0 +1,27 @@
+//! Representation of Cretonne IL functions.
+
+pub mod types;
+pub mod entities;
+pub mod condcodes;
+pub mod immediates;
+pub mod instructions;
+pub mod stackslot;
+pub mod jumptable;
+pub mod dfg;
+pub mod layout;
+pub mod function;
+mod funcname;
+mod extfunc;
+mod builder;
+
+pub use ir::funcname::FunctionName;
+pub use ir::extfunc::{Signature, ArgumentType, ArgumentExtension};
+pub use ir::types::Type;
+pub use ir::entities::{Ebb, Inst, Value, StackSlot, JumpTable, FuncRef, SigRef};
+pub use ir::instructions::{Opcode, InstructionData, VariableArgs};
+pub use ir::stackslot::StackSlotData;
+pub use ir::jumptable::JumpTableData;
+pub use ir::dfg::{DataFlowGraph, ValueDef};
+pub use ir::layout::{Layout, Cursor};
+pub use ir::function::Function;
+pub use ir::builder::Builder;