More bug fixing and a new build configuration.

Worked out the remaining silly bugs with selective symbol loading.
Added a test configuration. When executing 'dub build --config=test' the newest module 'util/source/app.d' will be included in the build an executable named 'DerelictUtil' will be output to 'util/bin'.
Removed the lib directory. Dub creates it automatically anyway.
Added .gitignore.