- Add a function to copy a slice to a C pointer and length.

  - Use it.

- Add macros to check that pointers are not NULL, to turn a pointer
    and length into a slice, to turn a C string into a `CStr`, and to
    interpret an OpenPGP fingerprint as a `Fingerprint`.

  - Use them.

- If `PepIdentity::as_mut` is passed a NULL pointer, return an error.

- Change `rust_str_to_c_str` and `rust_bytes_to_c_str_lossy` to
    return a `Result`.

  - Return `Error::OutOfMemory` if `malloc` fails instead of undefined
    behavior.

  - Update the callers to propagate the error when convenient and to
    panic explicitly when not.

    - Note: Rust panics if a memory allocation fails so we don't go
      too far out of the way to propagate memory allocation errors.

- Add a struct, MM, which holds the malloc and free implementation
    passed to pgp_init_.

  - Pass it to all functions that allocate using malloc or free memory
    using free.

- enumber 0.3 has been released.  It is no longer necessary to use
    an unreleased version.

- Instead of using the cookie in the Session data structure to point
    to the Keystore, point to a struct.

  - This makes it possible to have additional state.

- stringpair_t and stringpair_list_t will be needed by the
    implementation of pgp_list_keyinfo.

- Add the GPL v3 to COPYING.

- Fix the stale package config template.

  - Always generate it when building.

- What cargo wants, cargo gets.