after we split the solution into multiple projects the xml doc comments were no longer packed in the generated nuget package. in addition they were only generated for the net standard 2.0 target framework.
this change generates comments for all target frameworks and makes sure they're included in the generated package. it also adds missing doc comments where they weren't included on the public api and clears up a couple of minor formatting issues in the affected files.
by default nuget pack does not include project dependencies. this is suboptimal since it would require managing at least 5 nuget packages. this uses a workaround detailed here https://github.com/nuget/home/issues/3891 to copy the dependent dlls to the generated nuget package. this doesn't resolve the issue of how we publish the documentlayoutanalysis project, since it is the top of the dependency tree and we publish its parent, rather than it.
