Improved support writing attributes

[mikaelsundell]

First draft proposal for better header attribute management when reading and writing Aces EXR files.

[scottdyer]

@mikaelsundell Thank you for this contribution, and I apologize that this repository was not more actively maintained in the past. It was not under my direct purview, but I am trying to tidy things up now. I just wanted to retroactively acknowledge your attempt to contribute and appreciate your initiative in submitting a PR.

As part of the ACES project’s transition to the Academy Software Foundation (ASWF), I am closing all outstanding PRs before then formally archiving this repository to maintain a stable 'snapshot' for any legacy systems that may still depend on it.

However, if you are still interested in contributing to any other open-source tools or libraries in the motion picture arena, the ASWF is a much more robust and active community of developers operated by the Linux Foundation. I highly recommend checking it out if you still have any interest in contributing to open source projects.