Remove into_raw calls
Remove into_raw calls

Rather than consuming the `CString` and leaking memory, return a pointer
to memory managed by Rust. This is more valid as the `CString`s are
created in Rust in the first place.

mindriot101/rust-fitsio,mindriot101/rust-cfitsio,mindriot101/rust-fitsio,mindriot101/rust-cfitsio,mindriot101/rust-fitsio,mindriot101/rust-fitsio,mindriot101/rust-fitsio