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/reader/Cargo.toml

@@ -0,0 +1,15 @@
+[package]
+authors = ["The Cretonne Project Developers"]
+name = "cretonne-reader"
+version = "0.0.0"
+description = "Cretonne textual IL reader"
+license = "Apache-2.0"
+documentation = "https://cretonne.readthedocs.io/"
+repository = "https://github.com/stoklund/cretonne"
+publish = false
+
+[lib]
+name = "cton_reader"
+
+[dependencies]
+cretonne = { path = "../cretonne" }