Rename references from `master` to `trunk`

[jeffpaul]

Description of the Change

This PR builds on the creation of the trunk branch and changes previous references of master to trunk. Once this PR is merged, we can delete the master branch.

Alternate Designs

n/a

Benefits

Removes master branch as part of this repo.

Possible Drawbacks

none identified.

Verification Process

Searched repo for references of master, renamed them to trunk.

Checklist:

• [x] I have read the CONTRIBUTING document.
• [ ] My code follows the code style of this project.
• [x] My change requires a change to the documentation.
• [x] I have updated the documentation accordingly.
• [ ] I have added tests to cover my change.
• [ ] All new and existing tests passed.

Applicable Issues

n/a

Changelog Entry

n/a