Feature/i62 get ref points

[andybeet]

Justification 🐟

Need for an easy way to select reference points as a time series. To see the types of models used and the type of assessment conducted resulting in the reference point. This is a new feature

Types of changes

What types of changes does your code introduce? Put an x in the boxes that apply

• Bugfix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to not work as expected)
• Documentation Update (if none of the other choices apply)

Checklist/Reminders

Put an x in the boxes that apply

• I have updated relevant documentation?
• I have tested my changes?
• I have created unit tests and run devtools::test() to ensure all unit tests pass locally?
• I have run devtools::check() to ensure package builds locally?
• I have followed the proposed CONTRIBUTING guideline?

Further comments

Updates to NEWS.md and DESCRIPTION should be updated in dev branch in prep for versioning

Reviewer instructions:

Run pkgdown::build_site() locally and view the new functions documentation