Adds a package.json that works with the latest version of DUB

Hi! I forgot to answer in the corresponding thread in the DUB forum, but had this on the table for quite some time now.

DUB has just gained the necessary support to be able to have multiple DUB packages in the same directory. This allows to split up the different libraries into sub-packages that can be used as individual dependencies in other projects (e.g. using `"dependencies": {"derelict:opengl3": "~master"}`). If no sub-package is specified (i.e. `"derelict": "~master"`), then all libraries will be compiled in instead.

This pull contains a basic working package.json file, ready for registering in the registry, but it might use some additions in the authors/copyright sections that I wasn't sure about.