c-api-tools 0.1.0

Tools for the creation of C API bindings.
Documentation
# Making a release

To make a new release of bempp, follow the following steps:

0) If you are yet to make a release on your current computer, run `cargo login` and copy an API
   key from https://crates.io/me

1) Checkout the `main` branch and `git pull`, then checkout a new branch called `release-v[x].[y].[z]`
   (where `[x]`, `[y]`, and `[z]` are defined in the next step):
   ```bash
   git checkout main
   git pull
   git checkout -b release-v[x].[y].[z]
   ```

2) Update the version numbers in `Cargo.toml` and `c-api-tools-macros/Cargo.toml`.
   The version numbers have the format `[x].[y].[z]`. If you are releasing a major
   version, you should increment `[x]` and set `[y]` and `[z]` to 0.
   If you are releasing a minor version, you should increment `[y]` and set `[z]`
   to zero. If you are releasing a bugfix, you should increment `[z]`.

3) Commit your changes and push to GitHub.

4) Open a pull request and merge your changes in to `main`.

5) [Create a release on GitHub](https://github.com/bempp/c-api-tools/releases/new) from the `main` branch.
   The release tag and title should be `v[x].[y].[z]` (where `[x]`, `[y]` and `[z]` are as in step 2).
   In the "Describe this release" box, you should bullet point the main changes since the last
   release.

6) In the folder `c-api-tools-macros`:

6a) Run `cargo publish --dry-run`, then run `cargo package --list` and
    check that no unwanted extras have been included in the release.

6b) If everything is working as expected, run `cargo publish`. This will push the new version to
    crates.io. Note: this cannot be undone, but you can use `cargo yank` to mark a version as
    unsuitable for use.

7) In the root folder:

7a) Update the `c-api-tools-macros` dependency in `Cargo.toml` to `{ version = "[x].[y].[z]" }`.

7b) Run `cargo publish --dry-run`, then run `cargo package --list` and
    check that no unwanted extras have been included in the release.

7c) If everything is working as expected, run `cargo publish`. This will push the new version to
    crates.io. Note: this cannot be undone, but you can use `cargo yank` to mark a version as
    unsuitable for use.

8) Open a pull request to `main` to update the version numbers in `Cargo.toml` and `c-api-tools-macros/Cargo.toml`
   to `[x].[y].[z]-dev`

9) Add the release to the next issue of [Scientific Computing in Rust Monthly](https://github.com/rust-scicomp/scientific-computing-in-rust-monthly)