Complete documentation and build doc website

[jacobpwagner]

It would be helpful to have a website with a doc/API reference page for cytolib similar to the other cytoverse packages. For example, see the flowWorkspace site. This will require:

1. Completing the documentation in the form of Doxygen-compliant docstrings to enable easy building of corresponding HTML.
2. Weaving the generated documentation HTML in to a nicely formatted website. Again, Doxygen will make this much easier, but if we would like a similar format to the other doc websites we may be able to leverage pkgdown after the the doc HTML files are generated.

The first point is by far the more time consuming, but will pay off in the long run in terms of maintenance of the code base.