Update processing to comply with SPDX spec 3.x

### Description

This project was created when SPDX spec 2.3 was the latest version of the spec. It has since been updated to 3.x series. There are differences in the spec that do impact this project. For example, @deo002 raised a request in Issue #111 for support of operators that allow for all lower case or all upper case. This was not allowed under [spec 2.3](https://spdx.github.io/spdx-spec/v2.3/SPDX-license-expressions/#d2-case-sensitivity), but is under [3.0.1](https://spdx.github.io/spdx-spec/v3.0.1/annexes/spdx-license-expressions/).

### Acceptance Criteria

- [ ] Identify differences in 2.3 and 3.0 specs that impact this project
- [ ] Update the code to support 3.0
- [ ] Cut a major release