Rename 'cton_*' library names to match the 'cretonne_*' crate names.

This renames `cton_frontend` to `cretonne_frontend` and so on.

This fixes the first part of #287.

lib/filetests/src/lib.rs

@@ -10,11 +10,11 @@
 
 #[macro_use(dbg)]
 extern crate cretonne;
-extern crate cton_reader;
+extern crate cretonne_reader;
 extern crate filecheck;
 extern crate num_cpus;
 
-use cton_reader::TestCommand;
+use cretonne_reader::TestCommand;
 use runner::TestRunner;
 use std::path::Path;
 use std::time;