Improvements to the XMLDoc documentation comments

[ascpixi]

In a lot of areas of Cosmos, the XMLDoc documentation comments are either lackluster (e.g. being a transliteration of the member name) or non-existent. After improving the documentation comments, a more complete API documentation reference can be created automatically with tools like Doxygen or the current one used for cosmosos.github.io.

[quajak]

Since Cosmos is quite large, its impossible to do this all at once. It would be helpful if we track a list of areas, where the changes are especially impactful/important.