[Bug]: Clarify form of CompassDirection units

[CodyCBakerPhD]

What happened?

I made a CompassDirection with units rads instead of radians and the inspector issued a message - note the SI abbreviation is 'rad'

I could also see someone wanting to write "°" in place of "degrees" (and neither Python nor UTF-8 seem to prevent it)

Just wanted to confirm if we wanted to strictly enforce the form of these strings

Thoughts? @bendichter @rly @oruebel

Note: specific instance of more general discussion #208

Steps to Reproduce

No response

Traceback

No response

Operating System

Windows

Python Executable

Conda

Python Version

3.7

Usage

Command Line Interface

Were you streaming with ROS3?

No

Package Versions

No response

Code of Conduct

• I agree to follow this project's Code of Conduct
• Have you ensured this bug was not already reported?
• To the best of your ability, have you ensured this is a bug within the code that checks the NWBFile, rather than a bug in the NWBFile reader (e.g., PyNWB or MatNWB)?