Improvements:
- update ``pywnb`` and ``hdmf`` dependencies to use the newest versions. Also update supported python versions to include 3.7, 3.8, 3.9, and 3.10. dsleiter (24)
- specify that all source and detector positions should be measured in meters and update documentation accordingly. dsleiter (25)
- improve documentation. rob-luke (26)
- improve specs and enforce consistency of container class docstring and default description. bendichter, dsleiter (8)
- improve container class `__init__` docstrings and require keyword-only arguments. dsleiter (29)
- improve documentation and consistency in use of periods. dsleiter (30)