Move source files to source/ directory to support dub.
Basic DUB package.json file that builds a static library of dgraph.
Dgraph should be a source library for best use.
Move test demos to their own dedicated directory (needed by dub).

The Makefile tweak here is rather imperfect but works adequately.
Add test executables as dub subpackages.
Update Makefile to produce same output as dub.
Update README with build instructions.
Merge pull request #7 from WebDrake/dub

Fix Issue #5 - provide DUB packaging for Dgraph