This commit introduces a new, generic `.trix` file format, which is decoupled from any specific encryption algorithm.
The format is defined in `docs/trix_format.md` and consists of a magic number, version, a flexible JSON header, and a raw data payload.
A new `trix` Go package is implemented to handle the encoding and decoding of this format. Unit tests are included to verify the implementation.
An example file, `examples/main.go`, is also added to demonstrate how to use the `.trix` container to store data encrypted with the `chachapoly` package, showcasing the intended decoupled design.
