Licensing is unclear

`LICENSE.TXT` describes a dual NCSA/MIT licence, and the `README.md` agrees, but `Cargo.toml` declares "MIT/Apache-2.0". I note that `src/probestack.rs` also carries an MIT/Apache-2.0 dual licence.

Also, `LICENSE.TXT` refers to a `CREDITS.TXT`, which doesn't seem to exist.