Incorporate downstream CEGID changes.

[amcgregor]

Care of CEGID, my current employer, there are a collection of downstream changes utilized by the RITA job offer multi-posting platform. This pull request aims to homogenize the changes, eliminate the need to pin specific branches instead of released versions, and generally improve the project.

• General refinement re: Python 3 (namespace packaging, type annotation), cleanup, and corrected entry_points references.
• Improved example usage.
• Version and dependency pin updates.