Make sure all packages have a godoc comment

[magnusbaeck]

Description

Not all packages have a description, i.e. a "Package foo does this and that" godoc comment, but they should. Notably, the edition packages (editions/arica) are missing it but there might be others.

Motivation

A package description serves as a good introduction to the package. In the edition package case we could explain the purpose of the package and how it should be used as well as include a table with the (event type, version) pairs of the edition.

Exemplification

N/A

Benefits

See above.

Possible Drawbacks

None.