disable windows jobs until we have a windows runner again

  - 1.2.0 fixes a low-severity vulnerability.

  - See https://lists.sequoia-pgp.org/hyperkitty/list/announce@lists.sequoia-pgp.org/thread/SN2E3QRT4DMQ5JNEK6VIN6DJ5SH766DI/

  - `sequoia-openpgp` added support for Botan version 3, and made that
    the default for the `sequoia-openpgp/crypto-botan` feature.

  - Add the `crypto-botan2` feature to select the Botan version 2
    interface, and make that the default.

  - 1.16 fixes a few low-severity vulnerabilities.

  - See https://lists.sequoia-pgp.org/hyperkitty/list/announce@lists.sequoia-pgp.org/thread/SN2E3QRT4DMQ5JNEK6VIN6DJ5SH766DI/

  - When a branch is updated, kill any old jobs.

  - When generating `pep_engine_sequoia_backend.pc`, add the correct
    dependencies for the selected cryptographic backend.

  - Have the `sequoia-openpgp` always enable the `compression`
    feature, which is always needed.

  - Update memoffset to 0.8.0.

  - Update rusqlite to 0.29.0.

  - Update lru to 0.10.0.

  - This the version that is in Debian testing, and what
    sequoia-openpgp requires.

  - Move from the 2018 edition to the 2021 edition of Rust.

  - Add support to query whether the current cryptographic backend
    supports the specified cipher suite.

  - Fixes #28

  - Add a function to return some random numbers.

  - In C, it is usually okay to call a destructor, like `free`,
    with a `NULL` pointer: the function just does nothing.
    Implement the same semantics for `pgp_release`.

  - See #26.

Remove unneeded run conditionals so windows jobs will always run.

Set default rust toolchain since we don't specify in the repo.

Co-authored-by: Neal H. Walfield <neal@pep.foundation>

  - Update dependencies.

  - In particular, pull in nettle-sys 2.1.1, which fixes a problem
    building with the MSVC compiler on Windows.

Add a Makefile so that pEpEngineSequoiaBackend can be build using the
usual pEp style without directly invoking cargo, supporting the usual
targets build, install, uninstall, test, clean, all.
Make the project easy to install and uninstall, with a user-settable
prefix.
The Makefile is extensible with a local.conf file, of which we provide
an example.

Add CI support.

Add a .gitignore file.

Co-authored-by: Heck <heck@pep.foundation>
Co-authored-by: Neal H. Walfield <neal@walfield.org>
Co-authored-by: Luca Saiu <positron@pep.foundation>
Co-authored-by: Devan Carpenter <dvn@pep-project.org>
Co-authored-by: Volker Birk <volker.birk@pep-project.org>

  - Update `Cargo.lock` to get the latest and greatest.  In
    particular, buffered-reader 1.1.4 and sequoia-openpgp 1.13.0.

  - Require chrono 0.4.23 or newer, not exactly 0.4.23.

  - Enable static linking, which Android and iOS builds prefer.

  - See PEMA-103.

  - Fix deprecations.