Ignore constants discovered in passing

When RDoc parses a class body it will create new modules for newly
discovered constant namespaces.

When the constant isn't assigned-to the namespaces are now marked as
ignored which prevents them from appearing in the coverage report.

Bug #209
Create comment correctly for test
Ignore parents of nodoc classes

Bug #209
Don't ignore classes with documentation

This prevents a regression introduced by @5ba263c and @d96a7a7

Bug #209