Canon FD body-side mount

A Canon FD body side mount. Can be used to create adapters for FD lenses to other camera bodies and back-end lens caps for FD lenses.

I based it on a Fotasy adapter I have.

The `canon_fd_body_mount` module has two optional parameters:
- `grip` can be set to `true` or `false` (default is `false`). When set to `true` the mount will have a gripping texture
- `height` determines the height of the mount. The default is 7.5mm