Update cras_write() and test-cras_write() to resolve issue #17

[wikisqueaks]

Description

This pull request updates cras_write() and test-cras_write() to address formatting improvements described in issue #17.

• Added periods between authors in cras_write()to better align with journal expectations
• updated unit test test-cras_write()
• ran devtools::test() to confirm passes locally.
• corrected additional minor issue in get_roles() that was causing devtools::test() failure on clean checkout (inconsistent capitalization not in alignment with NISO html and the test-get_roles() function).

Notes for reviewers

The new implementation should maintain backward compatibility.

Please confirm the updated behavior matches the intended design outlined in the issue.

Fixes #17