Document return types in xml doc strings and improve documentation consistency/guidelines

[ncguilbeault]

While reviewing the PR: #48, @glopesdev pointed out that the "return" fields in the xml doc strings are not populated. It would be good to fill this information in with more useful information.

There is also a more general point here about consistent documentation in classes as well as articles. I can already see a few inconsistencies throughout. For instance, there are currently 4 separate LDS documentation articles (https://github.com/bonsai-rx/machinelearning/tree/main/docs/articles/LinearDynamicalSystems), but only 2 in the HMM package (https://github.com/bonsai-rx/machinelearning/tree/main/docs/articles/HiddenMarkovModels) and only 1 in (#48). Additionally, many classes in the Bonsai.ML.LinearDynamicalSystems package don't contain any information about parameters or return types (for instance,

machinelearning/src/Bonsai.ML.LinearDynamicalSystems/Reshape.cs

Line 30 in 3854f9e

public IObservable<double[,]> Process(IObservable<double[,]> source)

).

There is also quite a bit of redundancy between documenting values in "Description" attributes and also in XML docstrings. It would be useful to come up with a set of consistent styes/guides for documenting Bonsai.ML packages and perhaps Bonsai packages more broadly, particular around input/output types.