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/riscv/enc_tables.rs

@@ -0,0 +1,14 @@
+//! Encoding tables for RISC-V.
+
+use ir::{Opcode, InstructionData};
+use ir::instructions::InstructionFormat;
+use ir::types;
+use predicates;
+use isa::enc_tables::{Level1Entry, Level2Entry};
+
+// Include the generated encoding tables:
+// - `LEVEL1_RV32`
+// - `LEVEL1_RV64`
+// - `LEVEL2`
+// - `ENCLIST`
+include!(concat!(env!("OUT_DIR"), "/encoding-riscv.rs"));