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.

src/tools/main.rs

@@ -1,5 +1,5 @@
 
 extern crate cretonne;
-extern crate ctonfile;
+extern crate cton_reader;
 
 fn main() {}