How to get the code better documented?

@Spekular requested more documentation (or documentation *at all*) in our code. I can agree. But how do we assure that?

Our idea was to require coders to document those classes they work with. E.g. when I worked on the Lv2 plugin, I had to learn how the LMMS `Plugin` class works. Though I only changed a few code lines in it, I ended up [documenting the whole Plugin class](https://github.com/LMMS/lmms/commit/a1b355828e347b8e7fca8118873fc834953c1d67#diff-1840771aa9cc1d07324ea9a8059c8291). How to ensure that? We could simply add this to the [code review conventions](https://github.com/LMMS/lmms/wiki/Reviewing-Pull-Requests).

Any opinions, or other suggestions?

Start with the linked Reviewing Pull Requests wiki page and the referenced Plugin-class documentation commit. The issue seeks opinions on a documentation policy rather than naming a file, test, or specific change, so completion criteria are not defined; agreement on a process and where to record it would need to be established first.

Written by the indexing model from the issue text.