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.
The src/tools directory contains the cretonne-tools crate which will build
binaries for testing cretonne.
The src/libctonfile directory contains the ctonfile library crate which
provides reading and writing of .cton files.