Issue 9713 & 9714 - Ddoc bug fixes

[Issue 9713](http://d.puremagic.com/issues/show_bug.cgi?id=9713) - Ddoc: Empty description suppress automatic example generation
[Issue 9714](http://d.puremagic.com/issues/show_bug.cgi?id=9714) - Ddoc: Combination of -D and -unittest reveals hidden unittest function

Also added some refactoring change that I said in #1641.