Dub configuration to build demo `test.d` file added.


As of now on demo can be launched by `dub --config=demo` command from project root directory.
Proposing decent .gitignore
Had to tweak target type and import paths in order log4d could be referenced outside the project.
Merge pull request #1 from alaif/alaif/dub-config-for-test.d

Alaif/dub config for test.d