Documentation fixes and improvements

[iwanders]

I ended up on the documentation page for Linear which surprisingly didn't have any documentation on what that layer does. Only after reading the code did I see that the documentation lives in the module itself.

To test my newly added link, I ended up building the documentation, which showed several other warnings that I address in this PR as well, I'll comment why changes were warranted throughout my PR after I file it.

Edit: Forgot to say, but with these changes the documentation builds cleanly.