The problem is that adding more than one annotation on a barrel module breaks
the barrel. Thus, splitting the module up into more files solves this issue.
But it opens a new issue: you cannot as a consuming class only import the
annotations you want to use. Because the tests import the non-imported things
and then you end up with errors like:

ERROR: TestConversionWeight.mc:7: Unknown module OPN.Conversion.Weight in using
or import clause

This is unfortunate. It either means you import the whole barrel, or each
annotation should become a seperate barrel.

Signed-off-by: Wesley Schwengle <wesley@opperschaap.net>