Rename libraries

libctonfile -> libreader.

This library will only provide .cton file reading/parsing services which are
not needed after deployment.

Code for writing .cton files lives in the main cretonne library because it is
fairly small, and because it is useful for extracting test cases from a
deployed library.

cranelift/src/libcretonne/write.rs

@@ -2,7 +2,7 @@
 //!
 //! The `write` module provides the `write_function` function which converts an IL `Function` to an
 //! equivalent textual representation. This textual representation can be read back by the
-//! `ctonfile` crate.
+//! `cretonne-reader` crate.
 
 use std::io::{self, Write};
 use repr::Function;